Bantam wormdrive pinion

Hi I have just aquired a Bantam 1600 (AA 3061) and am trying to fix the lack of carrige drive and cross feed .

I have removed the apron and the gearbox ,although showing its age, does work.

Everything engages as it should except for the wormdrive pinion (labeled A in photo, and part 201-141 in diagram ). I cannot see how it was supposed to engage with the drive shaft (labeled B) inside it is smooth with no sign of a missing key , and the diagram does not show a key so if anyone knows how this was supposed to work I would be really grateful for some help . thanks , mike

I don't know the Bantam well enough to be definitive but I cannot think of any other feed shaft drive, with a keyway slot machined down it, that doesn't engage with a key within the pinion to provide carriage and cross feed drives.

Regards Brian

Can only echo what Brian says.

The power shaft, runnjing through the pinion has a keyway, implying that there will be a key to carry the drive from the shaft onto the pinion..

My inclination would be to strip the pinion off the shaft and out of the Apron, again, and examine very carefully for the remains of a key that has been sheared off, and to extricate the remains. If this is the case, there should be the other remains of the key still in the keyway of the shaft

If the bore of the pinion IS actually devoid of a key way, to ensure a drive, you have the task of making a keyway, either by cutting bone (With a slotting tool, racking the Saddle to and from with a suitable tool in the toolpost,, broaching, or filing ) and then making a key that is good, snug,fit in the pinion, and a sliding fit in the shaft keyway..

It will need to be prevented from coming out of the pinion, possibly by a washer at each end, or secures by drilling a tapping the key in the pinion to lock it in place..

(Can't see how it would be possible to cut a slot in the pinion bore for a Woodruff key )

Am alternative, but less satisfactory method would be to drill and tap the pinion for a number of grubscrewws which would substitute for a key.

Non preferred since the drive would be taken on several cylindrical faces rather that the one continuous linear one.of a proper key.

HTH

Howard

What is shown in the parts drawing for the feed shaft? that may show the key.

No point in making a shaft with a keyway all the way along it unless it drives something so the bit it drives must have a key somewhere. Long time since I took the apron off mine so I cannot be sure but would the key be cut integral with the pinion bush, pretty sure if it was a separate key it would be shown, one thing about Colchester’s is that their manuals and exploded diagrams were good. Not the end of the world though, it should be easy enough to cut or broach a keyway through if you have to, I would imagine the bits are soft.

Mike

Colchester call the drive shaft a spline shaft so its possible that the pinion was driven via a "single tooth spline" broached into the bore to stand proud of the support bushes. Easier to assemble than a loose key but vulnerable to shearing off causing loss of drive.

Clive

Edited By Clive Foster on 21/12/2022 17:08:56

Yep , I think mystery solved , I think you guys are right .

the key has worn away completly , and not shown in the drawing because of the angle , but can see in the forward /reverse handle diagram a key in the sleeve

Mike you should ask someone kindly to slot that for you on a shaper and fix a new key. Or go on youtube and ask John Mills (Doubleboost) if he could do it, I bet he would be glad to.

The Colchester lathe drive pinion and the on off lever dont have a separate key the bore of the pinion and the on off lever are broached to form the bore and key all in one piece if that makes sense so no separate key and they will wear away completely in time but they can be fixed by milling a slot through and fitting a key from the rear if that makes sense and tig weld in place, this is the same with all Colchester lathes, if you can pick up a spare worn item and fix it prior to yours wearing out, great as a spare because they always give up when you need them most. Good luck!

Hello again Mike,

I would be a bit concerned as to what caused the key to be worn away to vanishing point; it takes some loading to achieve that. You have some more investigation to do methinks which might have been the reason behind the sale.

Brian

If he does not have access to a welder, a thin sleeve on the outside glued in place with loctite would stop the key dropping out.

The pinion and on off lever wear out because of the particles of swarf etc in the keyways gets carried into these items as the machine is in use both being under load as the machine is working etc, bear in mind this is an industrial machine and has probably had a lot of use, I would think a good fix on this would last for years with light home use, it needs to be a good fix, make the new key as long as possible but more importantly a good fit into the pinion and secure or it will roll over in the keyway and jam or come out if you can tack in place or braze, also check the keyway for size as these wear as well, if worn and you have access to a milling machine clean up the keyway and make your key oversize, when repaired correctly these will last as long as the originals.

Got got to remember this machine is 50 + years old and has most probably worked its nuts off every day in an industrial environment, one of the problems I had with mine, which is the same vintage was the dog on the forward / reverse lever, the corners were worn off of it in the forward direction, convention seems to be down for forward, up for reverse, the easiest cure for me was to alter the wiring so forward is up. Machine only gets used once or twice a year.

This is an example of wear that all Colchester Lathes suffer from. My own Master 2500 fortunately had the feed pinion replaced a few months before I purchased it so it wasn’t an expense that I had suffer. However, what owners don’t often check is what wear has occurred to the feed shaft. When i checked the feed shaft on my machine the reduction in diameter was in the region of 0.025“ over a 12” length near to the chuck. I therefore reasoned that the bore of the pinion that was replaced before I obtained the machine was equally or more excessively worn. That should be considered when just simply milling a slot for a new key in the existing badly worn pinion. Incidentally I seem to recall that the surface of the pinion was hardened

Close examination of my feed shaft also revealed excessive wear in the keyway of the feed shaft. So excessive that, because of the wear found on the diameter, I decided to replace the shaft. Don’t get concerned about that though because the shaft is easy to duplicate. I bought a length of suitably sized silver steel which I turned the ends of on the lathe & milled the keyway on the Bridgeport.

I reasoned that a new key running in a worn keyway on a shaft that is undersized is going to be more prone to wear & runs the risk of earlier failure than happened previously. Therefore a worn shaft, running in a worn bore is going to be even more prone.

Here's an update on repair progress

I bored out some nylon to hold the pinion while i carefully bored out original brass bushes , stopping when wafer thin and peeling out last bit , then hammered in some 24mm nylon66 and bored that to match the cleaned up support bushes.

Then slotted pinion 3/16 to match spline in drive shaft , shaped and hammered in new key .

I have ordered oilite bushes to replace nylon and will put tiny TIG welds to replace retaining bolts at that point

the drive shaft needed minimal filing in a few spots to clean up , and its all running really well now

when that key wears out I can extract and replace

thanks again for all advice

Nicely done Mike. It'll be a while before you wear out that steel key

A most ingenious solution and one to remember for other similar drive key problems if we are allowed to use the idea. Thank you for telling us how you went about it---I especially like your planning ahead for the next time it needs doing!

Regards Brian

Thanks guys , but all credit to Colin who had the idea of the slot

Well done Colin, I made the cardinal error of not reading ALL the postings, one I see and deplore happening so often too. All credit to you then but it is still a clever idea.

Brian