Startrite Mercury 2 10 speed restoration

[RichardG]

This is going to be a very slow background restoration but I thought it may be of interest...plus it allows for suggestions of how to fix issues

The drill came from a local forge, sat unused in the corner for meany years as they’d upgraded to something much larger. It’s 3 phase. Everything worked and seemed to run OK, gearbox changed speed. The Chuck was chewed and no key so will need replacing, plus one of the arms had been replaced by a threaded rod. Here’s the drill as purchased, it was covered in grease and soot.


The strip down was fairly straightforward, the only issue was removing the quill key which led to be a bit of head scratching. In the end it was easy as it’s threaded and a few washes and a puller allowed it to be removed, this picture I found after the event on the Mig welding forum sums it up nicely.



you can see clearly why these drills are not as good as the Fobco/Meddings variants. The main frame although accurately machined is very lightweight when compared to a solid cast lump.



The other problem I found during the dismantling was the pulleys. The motor pulley has a chip on the largest pulley and the quill pulley was split. Both bits I somehow missed on the initial inspection. The thinness of the quill pulley is quite alarming, I’m amazed that this was seen as accceptable!



Next strip down was the 2 speed gearbox I immediately smelled a rat as after I had cleaned the grime off the socket heads showed signs of being removed. After getting to the internals I found 2 of the planet pinion gears damaged, and one of the planet pinion pins sheared. As there are 4 pinions the gearbox still works on the remaining 2 but this needs to be fixed. For info it’s part 70 & 71 on the drawing.


And here are the damaged gears.


These are not metal but made of some form of plastic, perhaps Tufnoll? I’ve been told by an engineering friend that this was quite common and ensured these failed first when overloaded to save the rest of the gearbox, not sure if that’s true or just Startrite penny pinching. The downside is that machine spares wants £45 each to replace, they’re less than 30mm in diameter This may write the gearbox off...However, I have been given the name of a company who can 3d print in a very hard wearing plastic or even metal if I can give them a cad drawing. The price for 3 gears would be less than £30 which is doable. I’ll be investigating this over the coming week unless anyone has a suggestions?

 

[porker]

What you were told is correct. Tufnol gears are quite common either as a fixed failure point or for better wear characteristics rather than metal on metal. Those look similar to the ones on my old Myford metal lathe. I wonder if you can get a more generic part as gears are measured according to their DP and are at least now more standardised. Not sure if older probably imperial stuff would be as easy to source.

 

[RichardG]

I‘m now learning the terminology of gears, never had to measure or specify one before, quite interesting. I’d be very surprised if it wasn’t a standard part and once I’ve sussed out the terminology and got the size I’ll have a web search.

 

[Yojevol]

If you need a DFX file for 3d printing get in touch. I would need the number of teeth on this and the mating gear and the distance between centres.
Brian

 

[J-G]

I wonder if you can get a more generic part as gears are measured according to their DP and are at least now more standardised. Not sure if older probably imperial stuff would be as easy to source.

'DP' IS older imperial --- and of course still in use --- 'Metric' gears are designated by their 'MOD'.

If those gears are the same as a Myford then they will be 20DP. The difficulty in getting replacements may be more to do with the Pressure Angle (PA). Being 'old' they are likely to be 14½º rather that the 'standard' today which is 20º but that is just conjecture on my part.

HPC Gears can supply Spur Gears in 20º PA from 96DP to 4DP in Delrin, Steel, Brass and Tufnol so might be worth an enquiry.

 

[J-G]

I‘m now learning the terminology of gears, never had to measure or specify one before, quite interesting. I’d be very surprised if it wasn’t a standard part and once I’ve sussed out the terminology and got the size I’ll have a web search.

Those gears are 20T so you can calculate the DP by first measuring the OD (in inches) and dividing 22 (T+2) by that. If the OD is 1.1" then they are 20DP, if it is 0.688" then they are 32DP and so on.

 

[J-G]

If you need a DFX file for 3d printing get in touch. I would need the number of teeth on this and the mating gear and the distance between centres.
Brian

You shouldn't need the centre distance or the tooth count on the mating gear Brian - you would need to know the PA though since that will affect the 'Base Circle' from which the involute curve has to be generated.

 

[Yojevol]

You shouldn't need the centre distance or the tooth count on the mating gear Brian - you would need to know the PA though since that will affect the 'Base Circle' from which the involute curve has to be generated.

The easiest way to generate involute gear profiles in TurboCad is with the info I have stated. I would have to assume a pressure angle.
Brian

 

[J-G]

The easiest way to generate involute gear profiles in TurboCad is with the info I have stated. I would have to assume a pressure angle.
Brian

I would be warry of the tooth form generated if there is no option to specify the PA in TurboCAD. It may well be that it generates an approximation of the Involute Curve that would satisfy the 'Pair' of gears being designed but not necessarily a good fit to an existing gear - which would have a true Involute Curve - so a single gear could either 'bind' or have excessive backlash.

 

[RichardG]

Thanks everyone for their replies and information. I’ve now done some measurements following the guidelines on Model engineer and J-G above.

then using the tables from the model engineer link to work out the pressure angle by measuring the span of 4 teeth then 3 and then 5.

DP 14.5° 20°
4 19.314 18.746
6 12.876 12.497
8 9.657 9.373
10 7.725 7.498
12 6.438 6.249
14 5.518 5.356
16 4.828 4.687
18 4.292 4.166
20 3.863 3.749 <<<<
22 3.512 3.408
24 3.219 3.124
26 2.971 2.884
28 2.759 2.678
30 2.575 2.499



Indicates that the pressure angle is probably 20 degrees.

Does this all sound reasonable?

 

[Sandyn]

The downside is that machine spares wants £45 each to replace, they’re less than 30mm in diameter

I think that's an OK price. Well worth it if you get the correct manufactured part/material and it gets the drill going properly again. When I priced replacement gears for my Meddings, it was something like £150+ for two, but a good bit larger.

 

[RichardG]

Following on this is the site I was pointed towards for 3d printing of mechanical parts.

Energy Chains, polymer bearings, flexible cable, & linear slides

They have an online cad tool for gears, but only for metric. However, just as a try, I worked out the Mod as if it was a metric gear and put the details into their cad. This was generated

I then overlaid this on a picture of the actual gear to give an idea how close it was.


I‘m not necessarily going down this route as although this confirms a reasonable shape it doesn’t confirm the absolute size but it was an interesting diversion.

 

[J-G]

Does this all sound reasonable?

Certainly.

My concern now (as far as getting a 'standard' replacement) would be the thickness and the bore sizes. From the original image you posted, I adjudge the thickness to be 0.5625" = 9/16" and the bore to be 0.375" = 3/8" BUT it looks as though there may be a sleeve - or even a roller bearing - at 1/2".

Looking at the HPC catalogue a 3/8" bore falls into their 'standard' but the width is also 3/8" for normal duty and 0.669" for heavy duty. My catalogue is a few years old but I've just checked on-line and the current price of a standard duty steel gear is £12.69 + VAT - you would have to make a 'specials' enquiry to determine the cost of a Tufnol version at 9/16" thick ---- and the detail of the bore needs addressing.

 

[RichardG]

Thanks J-G. I have now pressed out the centre bush, which I could almost do with my fingers. It’s split marked with 06 AGS 08?

The gear is 1/2“ thick and the bore is probably 15/32? The bush is 20 thou out of round if you measure several points.

 

[J-G]

Thanks J-G. I have now pressed out the centre bush, which I could almost do with my fingers. It’s split marked with 06 AGS 08?

The gear is 1/2“ thick and the bore is probably 15/32? The bush is 20 thou out of round if you measure several points.

No idea what 06 AGS 08 means but it looks to be a 'spring' bush which could well appear '20 thou out of round' with a simple measurement.

I would measure the bore rather than the bush to get a precise match and then ask HPC for a quote in whichever material you want to use. You can then use the spring bush in the new gear - it will probably need to be 'pressed' in. HPC will consider it a 'special' being 1/2" thick and an odd bore size but easily within their remit.

If you have a metal-working lathe you might be able to buy a 'standard' size and bore it out to take the spring bush and even add a 'washer' to one face to increase the thickness - - - That's certainly what I would do.

 

[RichardG]

Thanks again, I’ll make some calls next week.

 

[deema]

Measure the shaft it fits on, it might be 14/32 or 7/16” which is a standard size for an imperial oilite bush. Rather than a spring washer I’d be inclined to use oilite bushes

https://www.bearingboys.co.uk/?catid=2567&display=&orderby=&att1=7/16inch&att2=&att3=

 

[RichardG]

For info HPC gears quoted £70 for each planet gear each in 1/2inch Tufnol. I‘m chasing up a few final options before going to machine spares.

First, there‘s rumours of a local model engineer who has gear making facilities. Secondly, finding someone with a small CNC mill/engraver at home. I have some spiral 1mm cutters with a 3mm shaft which I think would be small enough to do the job at a low cutting speed. Finally, I may try cutting a blank on my little Simat 101 model lathe and then hand cutting the teeth.

For all options I need to source a small offcut of 12mm Tufnol, this will probably now have to wait until after Christmas.

 

[J-G]

For info HPC gears quoted £70 for each planet gear each in 1/2inch Tufnol.

Ouch! - that's a surprise.
Is the option of buying the 'standard' steel gear and boring it out not an option?

First, there‘s rumours of a local model engineer who has gear making facilities. Secondly, finding someone with a small CNC mill/engraver at home. I have some spiral 1mm cutters with a 3mm shaft which I think would be small enough to do the job at a low cutting speed. Finally, I may try cutting a blank on my little Simat 101 model lathe and then hand cutting the teeth.

The 1mm cutters will more likely have a 1/8" shaft - just a caution - but more pertinent, they will probably only have 6mm - 6.5mm maximum flute length so couldn't handle the ½" (12.7mm) gear width.

For all options I need to source a small offcut of 12mm Tufnol, this will probably now have to wait until after Christmas.

The thickest Tufnol I have on the shelf is only 10mm so I can't help there. I buy from Direct Plastics but their smallest sheet is 300mm sq and £45 + PP so hardly an option.

 

[RichardG]

Ouch! - that's a surprise.
Is the option of buying the 'standard' steel gear and boring it out not an option?

Yes, but the damage was probably caused by someone changing gear when the drill was running. The tufnol gears have saved the rest of the gearbox. Metal gears would work but if I absentmindedly did the same then...

The 1mm cutters will more likely have a 1/8" shaft - just a caution - but more pertinent, they will probably only have 6mm - 6.5mm maximum flute length so couldn't handle the ½" (12.7mm) gear width.

Thanks J-G, you know my toolbox better than I do!! I measured the mills and you‘re correct they actually only have a 5mm cutting depth and a 3.2mm shank.

The thickest Tufnol I have on the shelf is only 10mm so I can't help there. I buy from Direct Plastics but their smallest sheet is 300mm sq and £45 + PP so hardly an

There are a few smaller bits on eBay but thanks for looking. I’m also going to try Alt Saws and Spares to see how they compare to machine spares.

I‘ll keep dismantling and cleaning and confirm that nothing else is damaged before committing to any purchases.