Drummond 4" roundbed changewheel pins.

I intend to manufacture some changewheels for my old Drummond round bed lathe.

The few changewheels that came with the lathe are pretty battered, especially with the two pin locating holes. I am told that the two holes take tapered locating pins. It is very difficult to check, as at some stage, the holes appear to have been drilled oversize. As I intend to make a new set of wheels , I may as well do this as Drummond intended!

So the queries are,

1/ Do one, or both holes have a taper? If so, is this a standard taper like the usual 1 in 40 taper?

2/ If only one hole has a taper, then what was the original straight pin diameter?

3/ If both holes have a taper, then do they taper in the same or opposite directions?

I appreciate that it isn't too important to get the details correct (except maybe the answer to 3/). But no point in getting them incorrect and then finding that the wheels do not fit on other Drummond lathes!

Thanks for any information, as it does not seem to be readily available here or elsewhere.

Andrew.

Andrew, I've just checked one of my round bed gear wheels taken at random with the following results.

One hole is tapered and the other plain. The plain hole in my case comes out at 4.9mm which probably means a number 10 drill, but it won't cause any problems if you use a 5mm drill - the pins are a very loose fit in the plain hole. The tapered hole is for a 3/16 in. taper pin which being imperial will have a 1 in 48 taper, metric pins have a 1 in 50 taper. Again in reality I don't think it will affect their use if you opt for metric pins of an appropriate size - probably 4mm as metric pins are sized on the smaller end whereas imperial pins are sized at the the larger end. I gather imperial pins are difficult to obtain now so you might have to go the metric route anyway - unless you fancy making your own!

The length of the pin overall came out at 1.11 in, probably would be specified as 1 in. as the domed ends are NOT included in catalogue lengths, but that is likely to be variable as tapping the pins in and out of the gears tends to flatten the ends anyway. You really only need the pin to be a bit less than twice the thickness of the gear as if it's any longer there's a danger of it catching on the banjo when you're trying to drive a compounded pair if it sticks too far through the second gear.

If you stick to those sizes then there shouldn't be a problem with using your gears with any other "original" Drummond gears - at the age of the machines many of the gears around could well be "modified" as well as worn anyway.

The original pin (one per gear) was a No. 2 Imperial size, from memory when I tidied mine up. I turned some up myself from a bit of silver steel, although I'm sure mild steel would work just fine too. The large end of the taper goes in the gear. The small end protrudes out just less than one gear thickness and is a loose fit in the parallel clearance hole in the mating gear. The gears do come up on eBay fairly regularly if you wanted to buy rather than make, which is quite a project for a full set.

Edited By Hopper on 03/03/2017 02:53:52

Thanks for the information on the Drummond pins. I do intend to make a full set as I expect the ones that come up on Ebay are probably in the same condition as my existing change wheels.

I now have a shaper, courtesy of one of the advertisers on this forum and will shortly start making the required jig for involute gears, as discussed here on the beginners forum. I think the actual cutting can be accomplished in a few days. One lives in hope that it will work first time!

Regards,

Andrew.

Edited By Andrew Tinsley on 03/03/2017 17:43:48

Best of luck with the gear-shaping project, Andrew

Please keep us informed of progress.

MichaelG.

Hello Michael,

I have been on my back for the last couple (?) of days with acute sciatica. Now moving again thanks to some potent pain killer, that makes my normal morphine seem like aspirin. So NO workshop for me, this stuff is NOT compatible with moving machinery!

I now have Ivan Law's book on gear cutting, but no mention there of how to derive "d" (the bottom width of the "tooth" gap).

It seems that I will have to stop being lazy and work through the geometry of the involute gear form, to derive the correct formulae for "d" and then calculate from published data.

Mental acuity is definitely not at its best right now and I shall wait until I can leave off taking the medicine!

All the best,

Andrew.

Andrew,

I've just sent you an eMail

Take Care

MichaelG.

...

The small handful I have purchased from Ebay UK for my M-type Drummond have all been in excellent condition.

But if you have a shaper, it will make an interesting project for you. I imagine you could use the two disc method in Ivan Law's book to make a template to grind your shaper tool bit to.

Hello Hopper,

You don't need to cut a template for the shaper tool. All that is needed is a plain old HSS tool ground to whatever pressure angle you are using, plus the "bottom edge" ground off at the appropriate width that one would use for the bottom width of the gap, in an equivalent rack gear. I hope that makes sense!

If you rig up the shaper as discussed in a prior post, then that is all that one needs to do, in terms of making the shaper tool. The beauty of this system is that it will cut perfect involute gears. NO expensive cutters to buy or make and don't forget, a cutter is only accurate for one size of tooth. Using the shaper method, described previously, you get accurate gears cut for any DP.

If you have a shape,r then make up the required rotational jig (not difficult) and make perfect involute gears for any size you may want.

Andrew.