Advice wanted on drilling four special holes...

[Eric The Viking]

Above is a very simplified Sketchup model of my TS200 tablesaw. It's really old (but note the Freud blade ). I'm refurbishing it, and one key thing I have to do is replace the pivot for the rise and fall mechanism.

It's probably obvious how it works: the green pegs are the "trunnions" that allow it to tilt. So the blade tilts anti-clockwise as you look from this direction, to the left above the table). I haven't bothered to draw the tabletop, but it would be above the yellow part, bang next to the green pivots.

The purple part tilts up and down, pivoting about the red peg, raising and lowering the blade (Of course the riving knife has been removed for clarity! ;-) ).

Originally, the red pivot was a long roll pin. I thought spring steel was hardened, but apparently not: this one has worn significantly. I spoke to Axminster about the saw, and they have been very helpful. They've supplied me with a threaded, 6mm pin that they use (not sure if this is the current arrangement, but it's better than a soft Chinese roll pin!).

Here's my problem:

The holes in the yellow and purple pieces are fractionally under 6mm, and worn by the old roll pin so they're not circular. I need to get them to 6mm to fit my replacement pin, BUT I have to keep the alignment bang-on and not introduce any slop, as that will greatly interfere with the accuracy of the saw, propensity to kickback, etc. The axis of the holes has to stay exactly at right angles to the axis of the two green pins doing the pivot.

It's hard to measure those holes, as I don't have proper tooling to do so, but they are around 5.90-5.95 mm most probably. The U-shapes are about 3" across the wider part, and a snug fit with each other.

I have a drill press that's reasonable (has a nice Rohm chuck with relatively little runout, for a Chinese model), but that's it for machine tools. I was wondering about a long series drill, or whether I'd be better off drilling from both sides, or even starting again with a new set of holes.

Assuming I can make them accurately, new holes might throw off the riving knife rise+fall: there's a sort of parallelogram/pantograph arrangement so the RK moves parallel to the tabletop as you lift and lower the blade (not drawn it in).

One possibility is to put the old pin back in and temporarily tack-weld the edges of the U shapes together when they're in alignment. I can then ream or drill the holes (and grind off the welds again once done). At least then it wouldn't be worse than before (probably).

What do the team think? Is my best bet to buy some good quality long-series drills and go very carefully, or is there a another clever method of cleaning up and enlarging the holes to 6mm?

All thoughts would be appreciated!

Thanks, E.

PS: There's one extra complexity: I've simplified the purple part substantially for clarity: the U is actually rotated by 90 degrees roughly, so the "bottom" of it is towards the blade and motor; the datum plate that carries the motor and blade arbour is welded to the middle of the U (this is because of the riving knife arrangements). There's other metalwork inside both inner and outer U nearest the point-of-view of the 3D model, to do the tilt and rise+fall mechanics. I think I can still clamp it all up square (have some good small G-clamps), but space is a bit limited to get at things.

PPS: It would really benefit from a better pivot, but I have no idea how to go about that, and anyway, it's not exactly a Rolls-Royce table saw!

 

[Phil Pascoe]

A tenth of a mil is about four thou (sorry, my brain doesn't think in metric) - how much do you think the hole will go out of true if you just wipe it with some abrasive or a round file?

 

[Eric The Viking]

I hope not by much. A needle file will easily fit in the hole (and I have a few, including a diamond-grit one). Obviously I'm not going at it like a bull with a gate, but I'm still a bit nervous of ruining it.

The spot-welding thing only occurred to me whilst I was typing the initial post. The more I think about it, the more it seems a sensible approach - either that or drilling and bolting the two together temporarily. At least there's then no danger of anything slipping out of alignment.

 

[AES]

Eric, if it helps at all, I agree with phil.p, 4 thou is not a helluva big difference, and with all due respect to your TS, I doubt very much if the purple and light green bits are anything cleverer than "bent up" MS, albeit (hopefully) a bit thicker than the "normal" eighth inch or so one sees on many machines.

In which case, I venture to suggest that there is enough flex within that purple "U" shaped bit that it will flex under certain loads to the extent that the 4 thou will hardly matter - e.g. the walls of the purple part will close together slightly. (I'm assuming that the purple bit is a sheet metal fabrication and not a casting)?

But are you really stuck with that 6 mm pin you got hold of? Why not forget about that and simply use another pin of, say, 6.5 mm dia or so? Material and size of your choice, though I might think about silver steel. That would mean enlarging the holes in the purple and light green bit, but you could do that OK with your pillar drill, getting close to the final size you choose, then finishing off with a correct size hand reamer (which I assume you'd have to buy, but they're not horrendously expensive - e.g. Arc Eurotrade). The point is that you'd do the final hand reaming with all 4 holes "naturally" aligned.

And if you can do it yourself, or have a mate who can, you could even improve the basic bearing surfaces by adding some weld to the general area (inside surfaces of the purple "U", + if poss, to the outside surfaces of the light green). Procedure would be the same as above - drill to near size first, then finish off with a final size hand reamer, all 4 holes together.

Or, (not having a TS of my own) have I misunderstood the whole situation and offered a totally impractical/silly suggestion?

AES

 

[AndyT]

I agree that a reamer is the answer, not a drill, if you want nice round holes to exact sizes. I have a selection, which you are welcome to borrow, though they may be all imperial sizes - not a problem if you wanted to go up to 1/4" as suggested by AES (though he called it 6.5mm ).

 

[AES]

Sorry Andy T (and EtV)! Having been brought up "British" (engineering-wise anyway) but living in a Metric country now for 27 years (blimey, doesn't time fly!) I'm always getting my jums waddled up.

Having inherited a lot of Imperial tools when my Dad died, and having bought quite a few bits n pieces since then (mainly Metric) I can also probably help you with a loaner, depending on what size you need Eric - IF you go my suggested route that is.

AES

P.S. I STILL just cannot manage centimetres properly - mm and M are OK, but cm just confuse the hell out of me - still! My wife (Metric "born and bred") is always explaining that there are 10 mm to 1 cm - I KNOW that, that's easy, but I still get confused by the silly things (hammer)

AES

 

[Phil Pascoe]

Centimetres are the work of the devil and should be banned from use. :evil:

 

[AndyT]

Nothing to apologise for - I think it's essential to be able to flip from one system to the other, unless you want to ignore a) history, and b) the Americans ... oh dear, hang on a mo, that doesn't sound such a bad move, now I've written it down!

 

[AES]

Andy T says, " .... the Americans ... oh dear, hang on a mo, that doesn't sound such a bad move, now I've written it down! ...."

Yeah, fine Andy, but the trouble is I've spent at least the last 30+ years dealing with mostly US-built aeroplanes and that DOES "influence" me (in one way or another)!

AES

 

[chaoticbob]

Hi Eric, trying to open up a non-circular 5.9 mm hole to a circular 6.0 mm with a standard drill bit is unlikely to work. The bit takes the path of least resistance, then when it's had a bite decides to go back the other way and you end up with a bomb crater. Well, that's what happened to me when I tried something similar. Even if you did get an acceptable hole, when you hit the other arm of the U with a long series bit it would most likely wander.
You could possibly correct the hole eccentricity in on one arm by using a 6mm slot drill - these cut on the face (no leading taper to try and follow the existing knackered hole) and are much more rigid than twist drills. Then spot through with a long series centre drill and drill the other arm as normal. I haven't actually tried this on a drill press - success would depend on how rigid your quilll is. Just thinking out loud!
Robin.

 

[Blockplane]

My approach would be to enlarge the holes to 10mm or thereabouts and fit bushes .If you don't have a lathe to turn your own I'm sure you will find something on fleabay fairly cheaply.

You could make a couple of drilling jigs to guide the drill (just a hole drilled in a suitable piece of scrap) align them by fitting the bushes into them with a piece of 6mm rod running through both of them them, them clamp them in place while you drill.

 

[Rorschach]

As some others have mentioned, a reamer will do the job nicely. Get a spiral cut hand reamer in 6mm with a tapered tip.

 

[Phil Pascoe]

... I think it's essential to be able to flip from one system to the other

Many moons ago before the advent of the internet (on phones, at least) I went into the kitchen at work. He's here! Someone shouted. What's the problem? I asked. How many fluid ounces are there in a litre? 35 I said. We knew you'd know, brilliant, we can get on. A kitchen of eleven chefs, and none knew. Minutes before they'd had an argument whether there were two feet in a yard or three.

 

[AES]

Or, "how many litres in a gallon?" 4.54 is the answer (I have good cause to remember that - BUT, how many litres in a US gallon, as opposed to an Imp gallon?). Can't remember, I have to look it up - something about 3.8-something - I think!

None of this helps poor old EtV though!

P.S. I Like the idea of 10 mm bushes.

AES

 

[novocaine]

P.S. I Like the idea of 10 mm bushes.

who doesn't? thats a nicely trimmed bush.

bushing would be good but complete overkill (therefore an approach I'd adopt)

hand ream will be fine though or even a flag sander (a stick with bit of sandpaper wrapper round it so it flaps) and don't worry to much about it being slightly out, it won't make a massive difference.

 

[DTR]

As some others have mentioned, a reamer will do the job nicely. Get a spiral cut hand reamer in 6mm with a tapered tip.

Another vote here in favour of a 6mm hand reamer.

I do like the 10mm bush idea as it would make future repairs easier (or superfluous). But obviously it's more work, and relies on the bushes being reasonably concentric.

 

[Eric The Viking]

Dave et al, I agree. bushing it was my initial thought, possibly bolting on bronze bushes, so I could get the alignment spot on. But...

I had another look at the parts earlier (been a bit busy with work). I will post some proper pics - promise.

The existing holes are right in the corner of the inner "U" . I'd forgotten this and drawn it more sensibly in SU, with plenty of space around the pivot. I don't think there's actually room for bushes without moving the pivot point significantly. That might not matter, but it will probably affect the range of rise and fall, etc. I need to look a bit more carefully at the geometry - there are various parallelograms etc. involved for the plate that carries the riving knife and the rise and fall mech itself.

It's all a muddle of "I wouldn't do it that way!" bits, but then so is the Kity it's derived from and they're really pretty cheap considering how useful they are. And this one was almost free, which is why it's worth persevering to get it going again.

Thanks for all the thoughts. Everything is being read even if I'm not commenting all the time!

E.

 

[AES]

Quote:

P.S. I Like the idea of 10 mm bushes.


who doesn't? thats a nicely trimmed bush.


UNQUOTE:

Don't know what you mean novocaine :roll:

AES

 

[Inspector]

I'm probably in the minority but I would be tempted to look for European made roll pins, they do come in hard versions and variations of design and precision, and just replace the old one and use the saw again as is. I doubt you will use it enough to wear it to the point of being sloppy dangerous. It'll do until the next deal comes along in a better saw.

Pete

 

[AES]

@ Inspector: I agree to a point, and you're right, roll pins can be had in various hardnesses.

But purely personally, I thoroughly dislike roll pins, because A) although they go in easily, they're often a PITA to get out again (if needed of course), and B) they do (or course) have a spring action which is naturally tending towards "unrolling" the pin. That's why they have a tapered start end. But IMO, especially if the material they are being used as pivots for is "soft" MS, then that "opening spring" action tends to increase the wear on the pivoted material. Though I agree, a lot does depend on just how much rotation is involved - full circle, or even a half circle rotation, then IMO a roll pin is a real NO NO.

But I'm pretty sure that the OP's TS does not have anything like that much rotation, so "maybe".

But I still really dislike the things - they're "a cheapo accountants' solution" to a properly engineered pivot. Just personal.

AES