# Restoration and upgrade of an old Mini Mill



## sploo

A few months ago I got a decent deal on an old Warco Mini Mill (one of the many SIEG SX2 clones). I say it was a decent deal... but on firing it up, the motor emitted plumes of smoke, and the machine itself made some fairly horrific noises. I'd planned to strip it down anyway, so...

First the motor was removed, and the head taken off the vertical column: 







Looking inside the head it was clear the internal gearing was basically trash (apparently a common problem with this design):






I stripped more of the head:






And the gears at the top looked ok:






The motor was dismantled, and it turns out that a problem with the brush holders meant they'd damaged the commutator (smearing the metal and creating shorts). Fortunately I was able to clean it up:






Having looked into replacement gears I decided it would be better to attempt a belt drive conversion, so the shaft carrying the change gear had to be removed:











Finally, the spindle itself was pressed out:






And the last of the bearings removed:






Here you can see the spring loaded arm that balances the weight of the (now stripped) head. They're apparently not particularly even in the force they produce, so I planned to remove it and add a gas strut instead:






Many more images coming soon...


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## TFrench

Previous owner had no business being near that! 2 rocks to rub together would be his level I reckon.


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## sploo

Time to make pulleys for a belt drive conversion.

I got some 6082 T6 aluminium to make the small pulley that will fit onto the motor shaft:





















The larger pulley (for the spindle) was made from two pieces; otherwise I'd have had to remove a huge amount of material from large diameter stock.

First the large section for the pulley itself:






Then the smaller section:






The two were joined with some bolts:






Steps for the two pulley diameters:






Pulley grooves:






Central section bored out to fit the spindle:






Lacking any keyway broaches, I ground some cutters from steel:






And slotted the large pulley:






Then the small pulley:






More later...


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## sploo

TFrench said:


> Previous owner had no business being near that! 2 rocks to rub together would be his level I reckon.


To be fair, the motor problem might have been caused (by me) in transit, and when I looked into the internal gearbox issue with the SX2 clones I found it's a very common occurrence - hence the number of belt drive conversions!


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## sploo

With the belt drive conversion I needed a new way to mount the motor, using a swinging arm so the belt can be changed/moved/tensioned. First a prototype in plywood:











That seemed to work well, so onto a version from aluminium. Ignoring the warning sign, I fired up the CNC machine:






Basic parts before finishing:


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## sploo

The next steps were stripping down the rest of the frame; including all the dovetails on the axes:











And removing the old Z axis lifting mechanism:






Having removed the spindle for the old geared drive I would be left with a hole at the top and bottom of the head casting, so a template for a new cover was made:











Copied in HDPE plastic using a template following bit on the router table:






Bottom of the casting:






New cover fitted (with old cover in the background):






And the top:






Finally with the new pulley fitted. At this point I'd also drilled a pair of holes near the bottom of the pulley for a locking pin:


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## sploo

By this point I'd done a final clean up of the external parts, so it was time to begin putting the machine back together. First job was finishing the new motor mount, and also installing a locking pin holder (with a temporary, overly long, bolt):











Motor plate on the bottom of the motor, also showing the smaller pulley:






Fitted:






At some point I may make a knob for the motor mount screw (so the belt can be changed without using an allen key), but it's fine for the moment:


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## sploo

The next job was working out how to install a gas strut (for supporting the weight of the head). Little Machine Shop in the US offer a gas strut kit, and their strut is rated for 35lbs. 35lbs is 15.9kg (which seemed ballpark ok for the head on my machine), so I placed an order with SGS Engineering here in the UK. Their struts are ordered by Newtons, so I went for 155N as the closest "round number". The model I ordered is the GS8-18-280-310; though perhaps the next shorter version would have worked too.

Measuring out:






A block was drilled and tapped into the top of the head:






The rear of my machine has a thin metal panel, which I replaced with a sheet of HDPE plastic (assuming the strut might rub on the sheet):






On some of the newer SX2 clones the electronics box is on the rear of the machine and the top of the casting is open instead. As such, the strut can be mounted further forward (towards the head). The vertical column on this mini mill has a solid top, and there's a rib running through the middle of the inside towards the lower half. As such, it would've been difficult to put the strut inside the column.

With the strut being further away from the head I found that at the top of the stroke, the strut wants to bend out in the middle (away from the rear of the column) when the head is lowered. To prevent this I put together a "box" with some more HDPE to contain the strut and ensure it only runs vertically:






That seems to work pretty well. I have an alternate idea for the strut, but that's a job for the future.


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## Fitzroy

Great stuff, love the making of metal bits on the CNC. 

Fitz


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## sploo

Fitzroy said:


> Great stuff, love the making of metal bits on the CNC.
> 
> Fitz


Thanks. The CNC is really designed for wood and plastic, but it'll handle light cuts in aluminium if I'm careful.


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## AES

Very nice job sploo. Well done Sir!


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## sploo

Last set of "historical" updates.

One kit of parts for a mini mill:






Slowly going back together:











Time to look at the electronics. Neither bulb on the front panel appeared to be working, so time for a look:






The green bulb was dead, but I'd ordered a spare from Arc Euro Trade so I soldered that on. The orange/yellow bulb turned out to be OK, but one of the wires had broken off, so that was soldered back on too:






Having put everything fully together for the first time, a problem was evident. When the motor is swung back to tension the belt, the brush holder on the rear hits the rod supporting the head:






The rod could be moved back a few mm, but for the moment I just rotated the motor so the brush holders are on the sides. It means the cable now faces forward, but a cable tie or band should fix that:






And finally, all together, with a collet holder and bit:






That's about four months of work, on and off.

I have now done a bit of milling (aluminium and mild steel) and it's gone pretty well. Lots still to tune, but the machine appears to be working well.


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## sploo

Updates...

I finally got round to the "proper" solution for supporting the gas strut. Two pieces of mild steel were drilled and then bored:






A 12mm end mill was used to clean up the slot:






The ends (with the tapped holes) will later be cut off, and holes drilled in the top for attaching to the mill body:






The gas strut will ride inside a metal tube, but the gap between the strut and the mill body required a small flat to be milled onto the tube:






Parts cleaned up and ready for fitting:






A reminder of the current plastic guide for the gas strut:






All removed:






New system fitted. Grub screws are used to position the height of the tube:






Fully lowered:






Fully raised:






Another angle:






Early days yet, but it feels very solid, and the movement is really smooth - the head can be raised and lowered the whole travel with just one finger spinning the arm on the right side of the mill. I may blank off the remaining open section at the back of the mill at some point, and obviously clean up the over sized rod and metal bar that attach the gas strut to the head.

What's next? A taster...


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## AES

VERY nice work sploo.


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## sploo

AES said:


> VERY nice work sploo.


Thanks. It works surprisingly smoothly; but don't look too hard at the machining quality of the parts!

Certainly I'm learning the limits of the mini mill and mini lathe, and appreciating why the "proper" machinery is usually 10 to 20 times the mass.


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## paulrbarnard

Which collets did you buy? I have the same mill and would like to use collets rather than a chuck.

When I got mine the entire motor was loose, you could rock the top of the motor at least 10mm, resulting in a lot of noise. All the gears were is surprisingly good condition though.


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## sploo

paulrbarnard said:


> Which collets did you buy? I have the same mill and would like to use collets rather than a chuck.
> 
> When I got mine the entire motor was loose, you could rock the top of the motor at least 10mm, resulting in a lot of noise. All the gears were is surprisingly good condition though.


IRC It's an ER20 collet adapter with an MT3 taper (and importantly, M12 drawbar thread). I also bought a set of imperial and metric ER20 collects. All from banggood.

ER20 only goes up to a maximum of 13mm, so I also bought a 16mm MT3 collet for a cutter I have with a 5/8" shank (though it may be too big for that little mill).

You're lucky with the gears though; I understand they're essentially a "consumable" component. If you're fortunate you break one on the top. If you break the internal gears you're in for a very long day. Given that the internal gears were lunched on my unit I opted to do the belt drive conversion.


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## RichardG

Excellent work. With the skills people have on here I can’t help but wonder if this group couldn’t design and build its own set of community machines and then have them manufactured....

A couple of questions about the gas strut. Can you mount them either way up or does the cylinder have to go on top? Is the force applied in a linear fashion, I.e. is the resistance the same when fully extended or compressed? I’m looking at ways of supporting a Startrite drill head and a gas strut is one option....

thanks.


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## sploo

RichardG said:


> Excellent work. With the skills people have on here I can’t help but wonder if this group couldn’t design and build its own set of community machines and then have them manufactured....
> 
> A couple of questions about the gas strut. Can you mount them either way up or does the cylinder have to go on top? Is the force applied in a linear fashion, I.e. is the resistance the same when fully extended or compressed? I’m looking at ways of supporting a Startrite drill head and a gas strut is one option....
> 
> thanks.


I think generally they're intended to be used with the thinner rod facing upwards, but it doesn't actually matter. However, the advice for mills is that by facing them downwards there's less risk of it clogging up with chips or dust.

The force is surprisingly linear (unlike the spring loaded arm that was originally fitted). As noted; I can raise and lower the ~16kg head on the mill by spinning the rotating arm with a single finger. 

Work out the weight of your drill head in kg and multiply by 9.81 to get a suitable force value in Newtons (e.g. with my 16kg head I went for a 155N strut as close enough).


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## AES

sploo said:


> Thanks. It works surprisingly smoothly; but don't look too hard at the machining quality of the parts!
> 
> Certainly I'm learning the limits of the mini mill and mini lathe, and appreciating why the "proper" machinery is usually 10 to 20 times the mass.



Yup, it really IS true about "price". With my "budget" (!) one of the things I'm still having to learn (lathe only, me, no mill) is that you really DO need to appreciate how the light-weight components lead to inherent lack of "real" rigidity. But if one isn't in a hurry (what's 4 x 10 mm cuts against 1 x 40 mm cut?) is that it's "only" my time! No real problem, and I don't have the space for "proper" machines anyway.


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## sploo

AES said:


> Yup, it really IS true about "price". With my "budget" (!) one of the things I'm still having to learn (lathe only, me, no mill) is that you really DO need to appreciate how the light-weight components lead to inherent lack of "real" rigidity. But if one isn't in a hurry (what's 4 x 10 mm cuts against 1 x 40 mm cut?) is that it's "only" my time! No real problem, and I don't have the space for "proper" machines anyway.


It's probably more true of lathes than mills (as there are quite a few sizes of "home" mills now) but my mini lathe is ~40kg and 80cm long. A lathe that was 1m long and 120kg would be acceptable for a small home shop, have a bit more capacity, and would be much more rigid due to the mass.

The problem is that most of the old lathes for sale are either of the "mini" variety, or north of 1000kg!


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## paulrbarnard

sploo said:


> IRC It's an ER20 collet adapter with an MT3 taper (and importantly, M12 drawbar thread). I also bought a set of imperial and metric ER20 collects. All from banggood.
> 
> ER20 only goes up to a maximum of 13mm, so I also bought a 16mm MT3 collet for a cutter I have with a 5/8" shank (though it may be too big for that little mill).
> 
> You're lucky with the gears though; I understand they're essentially a "consumable" component. If you're fortunate you break one on the top. If you break the internal gears you're in for a very long day. Given that the internal gears were lunched on my unit I opted to do the belt drive conversion.


I just pulled mine out to check and it is MT3 with 12mm. I just ordered an adaptor and collets from Banggood.


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## Davey44

Well done you! A man after my own heart!


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## sploo

I started fitting the glass scales...

With the X/Y axes carriage removed, it was a simple job of drilling and tapping holes to fit the scale for the X axis. It's offset to the side to avoid the coolant drain port. The image shows the rear of the carriage:







The small red plastic tabs restrict the range of movement but they're present to help ensure the two parts of the scale are aligned correctly...






...and they're easy to remove once the hole locations are set:






Next it was on to the Z axis. It would have been less work to position the slider of the scale facing to the front, but then the slot in the main body of the slide would be exposed to chips. The left side of the head has an M8 tapped hole that was for the old spring based lifting mechanism (replaced with the gas strut), and an M6 tapped hole would also become available once the (now useless) arrow indicator was removed:






A bit of bodging with some aluminium plate went surprisingly well (other than being very soft and "gummy" to drill), and I needed a couple of spacers (basically thick washers), which were turned on the mini lathe. Then I dropped one. Which of course instantly entered another dimension and could not be found. So I had to machine another :






Bit of a random assortment of screw heads, but it's what I had in the right sizes:






X and Z scales working well; though I've not made any attempts to indicate them in yet:






The Y scale will require a bit of thinking. It would be easy with it the "wrong" way up; but that would definitely get the slider full of chips. I'll have to make another aluminum bracket, but I need to work out how to mount it without fouling the holes to bolt the machine to a worktop or restrict X axis movement.

The sliders do come with aluminium cover plates BTW, but there's not enough space for them on the mini lathe (plus it wouldn't work on the Z axis with the aluminium bracket passing over the top).


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## paulrbarnard

sploo said:


> I started fitting the glass scales...
> 
> With the X/Y axes carriage removed, it was a simple job of drilling and tapping holes to fit the scale for the X axis. It's offset to the side to avoid the coolant drain port. The image shows the rear of the carriage:
> 
> 
> 
> 
> 
> 
> The small red plastic tabs restrict the range of movement but they're present to help ensure the two parts of the scale are aligned correctly...
> 
> 
> 
> 
> 
> 
> ...and they're easy to remove once the hole locations are set:
> 
> 
> 
> 
> 
> 
> Next it was on to the Z axis. It would have been less work to position the slider of the scale facing to the front, but then the slot in the main body of the slide would be exposed to chips. The left side of the head has an M8 tapped hole that was for the old spring based lifting mechanism (replaced with the gas strut), and an M6 tapped hole would also become available once the (now useless) arrow indicator was removed:
> 
> 
> 
> 
> 
> 
> A bit of bodging with some aluminium plate went surprisingly well (other than being very soft and "gummy" to drill), and I needed a couple of spacers (basically thick washers), which were turned on the mini lathe. Then I dropped one. Which of course instantly entered another dimension and could not be found. So I had to machine another :
> 
> 
> 
> 
> 
> 
> Bit of a random assortment of screw heads, but it's what I had in the right sizes:
> 
> 
> 
> 
> 
> 
> X and Z scales working well; though I've not made any attempts to indicate them in yet:
> 
> 
> 
> 
> 
> 
> The Y scale will require a bit of thinking. It would be easy with it the "wrong" way up; but that would definitely get the slider full of chips. I'll have to make another aluminum bracket, but I need to work out how to mount it without fouling the holes to bolt the machine to a worktop or restrict X axis movement.
> 
> The sliders do come with aluminium cover plates BTW, but there's not enough space for them on the mini lathe (plus it wouldn't work on the Z axis with the aluminium bracket passing over the top).


You are going to cost me a lot of money. This is now on my list...


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## sploo

paulrbarnard said:


> You are going to cost me a lot of money. This is now on my list...


*LOL* Sorry 

At least based on a quick test you can move the axes accurately to the 0.005mm accuracy (i.e. you can hit an exact value). Whether that little mini mill could actually cut something with 0.005mm accuracy is another matter.

Mostly I want it for accurately drilling hole patterns for motor mounts and other similar jobs, so it should be OK for that.


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## sploo

It's been more than a month, but I've finally finished the Y axis.

The only way it was going to work was to mount the scale on its side; which also means it's the wrong way up (in the sense that there are recesses for screws, but they're now on the bottom). Flipping it over would have resulted in the cable hanging out of the front:






I modified one of the aluminium covers that came with the scales to shield the gap between the scale and carriage. It removed some of the anodising, but that's just cosmetic:






Next a pair of small spacers were made on the lathe:






Then another bent alum plate to bridge the carriage to the axis:






The handwheel just clears all parts, even with the X axis fully to the right:











In a more normal central position there's plenty of room:






To fix the display I made a couple of small blocks to mount the arm bracket, as the ideal height puts the bracket over my gas strut:






For the moment I've just wrapped the (long) cables round the arm. They could do with reducing, but it'll be a lot of soldering to do all the internal connections, so for the moment I'll see how things go:


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## AES

Really neat job sploo. Well done Sir.

Of course if I was a nit picker (which I'm not !!!!!!!!) the little ali cover you've made to cover the gap at the carriage COULD have the 2 mounting holes on the vertical face extended slightly into vertical slots - OR have the height of those 2 spacers you made reduced slightly. Either of those would then allow the horizontal face of the bridge to be really horizontal and not slightly tilted backwards.

But that would be REAL nitpicking and as long as the lower edge of that cove doesn't rub against the anodised ali cover below it, no harm done.

(Yup, I'm really being a clever Dick here mate, and just to be clear, in this post my tongue is stuck so far into my cheek that I look even more lop-sided than I usually do).  Nice job.


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## sploo

AES said:


> Really neat job sploo. Well done Sir.
> 
> Of course if I was a nit picker (which I'm not !!!!!!!!) the little ali cover you've made to cover the gap at the carriage COULD have the 2 mounting holes on the vertical face extended slightly into vertical slots - OR have the height of those 2 spacers you made reduced slightly. Either of those would then allow the horizontal face of the bridge to be really horizontal and not slightly tilted backwards.


If you look at the bottom right of the first image you'll see that the screw holding the scale down protrudes above the side of the scale (because the recess for the mounting screw is on the other side). Unfortunately that means they foul the cover, so I couldn't mount it any lower.

I think I'd get away with the cover being perfectly square as there's just enough clearance under the bridge between the carriage and the axis, but I don't have a sheet metal brake so the ally bending was done... errr... "freehand". But, you know 93 degrees has to be better than 90, as it's bigger, right?


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## AES

Understood. As said sploo, I really was only pulling ye leg mate (I was just excited 'cos I noticed something - nice pix BTW).

Edit for P.S: I thought that was 89.5 degrees!


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## sploo

AES said:


> Understood. As said sploo, I really was only pulling ye leg mate (I was just excited 'cos I noticed something - nice pix BTW).
> 
> Edit for P.S: I thought that was 89.5 degrees!


I spent a long time swearing at those screws 

FYI I think the smaller bridge is actually (almost) square. It's the guard that's not in the same postcode


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## AES

sploo said:


> I spent a long time swearing at those screws
> 
> FYI I think the smaller bridge is actually (almost) square. It's the guard that's not in the same postcode



Yeah, I spotted that (89.5 degrees, just like I said)!!!!!!!!!!!!!

OK mate, I'm going to stop this, I'm just being silly now - really. And seriously now mate, nice job!


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## sploo

AES said:


> Yeah, I spotted that (89.5 degrees, just like I said)!!!!!!!!!!!!!
> 
> OK mate, I'm going to stop this, I'm just being silly now - really. And seriously now mate, nice job!


No worries. I'm pleased to have finally finished it (apart from all the things that still need doing, obviously), but the scale on that last axis is certainly the one that's a bit of a cludge. I'm not pretty either so I'll live with it


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## Fergie 307

Nice job. I have the next size up, an Amadeal 25. Fitted a Chinese two axis kit to it £170 from a guy in Hong Kong on e bay. My machine has a built in dro on the quill. Slightly more room on mine so was able to fit the encoders upright. I was so impressed with the kit I bought another for my Harrison lathe. But a problem in that the large encoders that come with it wouldn't fit neatly on the cross slide. I ended up buying a single slim encoder from Warco for the cross slide. The plug wiring was different so had to rewire it for the correct configuration for it to work with the kits display, both the kit and the Warco slide come with pin out information for the connector so it's easy enough to work it out. Have shortened the cables on both set ups so don't have umpteen feet of extra cable. Even with the extra Warco encoder it was still a lot cheaper than most kits. Both have worked a treat for over two years, and are within the spec as far as accuracy is concerned. I have also fitted a power cross feed to the mill. Looked at the ones sold specifically for it by Grizzly etc. Seem to be a lot of problems with these, and most only seem to give a minimum feed rate of about 80mm/min, not sure what use that is to anyone. After some head scratching I used a unit designed as as Bridgeport type table feed. These are available with a lot to mount them horizontally on the left hand end of the table of my machine, but it's a bit of a bridge up to my mind. I have used a similar idea but with the unit mounted as it were upside down on the right hand end of the table. This means you can mount it so it is level with the table, rather than sticking up above it as in the manufacturer's version. Had to make the brackets and an adaptor to link it to the screw. Massively powerful unit, and with very low gearing, so with it turned right down you can get 10mm/min or less as a minimum feed rate. The other advantage of this type of feed unit is that you can still use the manual wheel without having to have clutches or anything. Many of the aftermarket kits don't allow for that.


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## sploo

That Amadeal 25 looks nice, but it's a bit rich for me 

All the bits for the scales and display cost me about £250 (from Banggood). The mill (used, from eBay) was £300, and the gas strut I think was around £30; so ignoring the accessories and small cost of aluminium stock I'm out about £600. Not cheap, but I guess that's a decent price for a small mill with a 3 axis DRO.

I suspect that a power feed will be the next thing I look at - though I've found that a nut driver on a cordless drill works OK as a temporary solution.


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## Fergie 307

As you say a good price for what you have. I was a bit dubious about the kit, but the seller had good feedback so I thought at that price I would give it a punt. Pleasantly surprised by what turned up. The only thing I didn't like we're the cable ends, which were cheap plastic cased ones. When I shortened the cables I took the opportunity to change them for decent metal ones, they're only a couple of quid each. If you go for the power feed do look at the feed rates. I am sure there are people who would find 80 off mm/min ok. I do a lot in stainless, and sometimes removing quite a lot of material, so like to take it gently out of respect for what is still a relatively small machine. Not sure there would be room to fit the one I have to yours, when I get a moment I will post some pictures. The single Warco scale cost £80, and I can't say was of noticeably better quality than the ones in the kit, either externally or looking at the board inside it. In fairness the Warco did come with a much better assortment of brackets, and the slim scales are always more expensive anyway.


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## sploo

Fergie 307 said:


> As you say a good price for what you have. I was a bit dubious about the kit, but the seller had good feedback so I thought at that price I would give it a punt. Pleasantly surprised by what turned up. The only thing I didn't like we're the cable ends, which were cheap plastic cased ones. When I shortened the cables I took the opportunity to change them for decent metal ones, they're only a couple of quid each. If you go for the power feed do look at the feed rates. I am sure there are people who would find 80 off mm/min ok. I do a lot in stainless, and sometimes removing quite a lot of material, so like to take it gently out of respect for what is still a relatively small machine. Not sure there would be room to fit the one I have to yours, when I get a moment I will post some pictures. The single Warco scale cost £80, and I can't say was of noticeably better quality than the ones in the kit, either externally or looking at the board inside it. In fairness the Warco did come with a much better assortment of brackets, and the slim scales are always more expensive anyway.


I did take one of the scales apart to see if I could reverse it for better fitting on the Y axis (no cigar with that design) but I was reasonably pleased with the look of the internals. I strongly suspect the units sold here will be ultimately made in the same Chinese factories anyway.

Given what I've found from the mill so far, it'll need a very low feed rate for anything but aluminium. It makes you realise why the "proper" machines are in the 1 ton+ weight category.


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## Fergie 307

So this is my power drive setup. Excuse the poor quality of the pictures. The bracket was cut from a section of 125 x 65 steel channel and then machined to remove the fillet inside the angle and give a mounting surface for the unit. The only real grief was making the coupler. It has a blind keyway. I haven't got a broach small enough so ended up grinding down a carbide tipped parting off tool to do it. Otherwise fairly straightforward. The alloy block you can see houses a ball race to support the end of the shaft.


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## sploo

Nice. Is there a clutch, or does it just not mind being back-driven when you use the handwheel at the other end?


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## Fergie 307

Yes it back drives quite happily so no clutch.


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## sploo

Slightly off topic from the original restoration, but it's the first use "in anger" of the mill + DRO...

I needed to make a screw for an early Stanley Bedrock 604 1/2 I've been restoring. The screw was turned on the lathe, and mounted in a rod with a tapped hole. The mill came with a selection of slitting saws, but no arbor, so I knocked one up on the lathe and found the blade best suited for the screw head slot.

The DRO made it really easy to touch off on the sides of the screw head to set the centre height, and get the slot depth just right:







Nothing particularly special, but it's the first screw I've made from scratch:






And it even fits:


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## AES

And that's a very "nice-looking" screw. Well done Sir!


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## sploo

AES said:


> And that's a very "nice-looking" screw. Well done Sir!


I'm just glad I didn't "screw" it up.





I'll get my coat.


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## MARK.B.

And it even fits:

My better half often mutters under her breath something about me having a screw loose, any chance you could make another one that fits and pop it in the post


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## sploo

MARK.B. said:


> And it even fits:
> 
> My better half often mutters under her breath something about me having a screw loose, any chance you could make another one that fits and pop it in the post


Ah, but do you need a left-handed 3.65/8" Whitworth screw in 47.2TPI... or an M8?


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## MARK.B.

Not sure best to send a selection  being an older model i think probably imperial with with a coarse thread


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