MEW 221: Bravo!

[HopperParticipant @hopper]

[HopperParticipant @hopper]

Was so gobsmacked to see an article about the beloved old Drummond M-type I had to order a copy to be sent airmail to me in Oz. I thought the old Drummond was a thing of the past in this brave new CNC world.

Wonderful article and pics by Geoff Walker, going a step further than the old Bird/Papworth method.

I'm wondering if Geoff is a member on the forum, could he tell us a bit more about his M-type? In particular, what was involved in fitting the ML7?-style bridge to the cross-slide lead screw to get that little bit of extra movement that the M-Type so badly needs?

And is that some kind of wiper, or odd chamfer on top of the carriage at the rear in the pic showing the telescopic gauge in place on the leadscrew? Something odd looking there and inquiring minds want to know.

Or perhaps a further article on his M-Type mods might be in order?

Quite enjoyed the rest of the mag too. Seemed to have more of interest to me than the last issues I saw on the newstand, going back some time now. Seems to be a good mix of old and new technologies from the Drummond to DRO for the X3. And a good mix of the long and short, series and one-offs. Particularly liked Harold Hall's hint on the V-block alternative. But then, I like just about everything Harold has ever written.

A resounding Well Done! to the team putting the mag together.

I might even take out a subscription as an early Christmas present to myself. The Man and His Lathe series sounds interesting. Hopefully there will be a Drummond or two amongst the mix?

[Neil WyattModerator @neilwyatt]

Thanks Hopper,

I don't want to dampen the flames of enthusiasm, but no Drummond lined up yet, but if Geoff (or someone else) would like to offer?

Neil

[EugeneParticipant @eugene]

Hopper,

I'm very much a newcomer to home machining, but my recent choice for a lathe was an M type.

The only mod I've done thus far is to fit an exterior thrust bearing between the headstock phos bronze bearing and the original threaded pressure bush. All signs of the chatter that previously existed has gone and I can take some pretty daunting cuts.

I snatched up a second M type just recently, a long bed version this time, as much for all the goodies and accessories that came with it as anything else, but overall it was in much better nick than I thought it would be. The leadscrew half nut however is very worn and so like you I was interested in Geoffs article in MEW 221.

I was a bit taken aback when he said that he wasn't going explain how to make a left handed internal Acme thread because it was all in the text books. No doubt it is but this greenhorn could have done with someone holding his hand!

It did strike me at the time I was playing around with the M type spindle bearing adjustment and headstock disassembly that a poor man's guide would have been a handy thing … it isn't at all like the manual says, and there are a few wrinkles.

Do you have a M type down under?

Eug

[HopperParticipant @hopper]

Eugene, yes I have a 1937-ish M-type that is my only lathe and in regular use.

LH thread is simple enough. On the Drummond it is a square thread, not Acme. I made a "bobbin" for mine in the Drummond itself. Being an 8TPI thread you run the same size gear on the mandrel and on the leadscrew. I think I used a pair of 40 toothers. then by running one large idler gear between them (70T etc) you get the leadscrew turning the "wrong" way so the carriage moves away from the headstock when under power. No need to use chaser dial etc.

The thread is 8TPI x 3/4" diameter. So thread width and depth for a square thread is worked out as: 8TPI = 1/8" pitch. Pitch includes one tooth and one "valley". Therefore the "valley" you are going to cut is 1/16".So I ground up an internal boring bar toolbit to be .064 wide — allowing .002 working clearance. Toolbit is ground up much like a small parting tool. Flat on top. Relief angles on front and both sides. The leading side (right hand when looking at it in place on the lathe) needs extra clearance to clear the helix angle of the thread. Check your toolbit in the thread on the leadscrew to make sure it fits and has clearance.

Internal diameter of the bobbin is drilled then with a small boring bar opened out to .625" diameter (3/4" minus two thread depths of 1/16&quot. I added a bit of working clearance and bored mine to about .630" diameter.

Then I mounted the square toolbit in the largest boring bar that would fit in the hole and still allow a little over .062" protruding. About 7/16" diameter IIRC.

Now the tricky bit. Being a lefthand thread, you have to wind the tool in to the hole right to the back until it comes out the other end of the hole, nearest teh headstock. Then with lathe in backgear nice and slow, wiind cross-slide out gradually until tool just kisses the bore of the hole. This is your zero setting. Mark it with a felt pen. Finished thread depth will be .062" out from this.

Start the lathe. Wind cross slide out say .005", engage the dog-clutch and take a cut. When the toolbit appears out of the righthand end of the hole, disengage dog clutch, wind tool back in PAST the zero point, wind carriage back to the left until toolbit clears end of the job. Wind cross slide back out to the zero point, this time plus, say, .010".

Repeat repeat repeat etc until you have wound the cross slide out to .062" past the zero point. I added a few thou of working clearance here too.

Ideally one should check the thread for fit by screwing a piece of leadscrew into it at this stage. I did not have a spare leadscrew, so added the tad of working clearance to all dimensions to be sure it would fit. As the nut is to be cut in half using a hacksaw (after marking up by running a lathe toolbit up the length of it while still chucked up to scribe a guideline either side) radial measurements are not critical. Main thing is to make sure the width of the threaqd cutting toolbit is a couple thou wider than the thread on the unused part of your machine's leadscrew. (the far right hand end). If you make the toolbit too narrow, the resulting thread will never fit on the leadscrew.

Whew, a lot of words, but a simple process really.

Have fun!

PS, long bed eh? Nice one. No more jagging your hand on the live centre while taking jobs in or out of the chuck.

[Oompa LumpaParticipant @oompalumpa34302]

At the risk of going all "20th Century" on you, I wouldn't bother with all of the above (no disrespect) but I would simply make a new Leadscrew half nut using Delrin or similar and just heat the leadscrew up and crush the Delrin around it.

This I have found works well.

graham.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Oompa Lumpa on 17/10/2014 10:19:58:

At the risk of going all "20th Century" on you …

.

Any 21st Century alternatives ?

MichaelG.

[Neil WyattModerator @neilwyatt]

Posted by Michael Gilligan on 17/10/2014 10:38:43:

Posted by Oompa Lumpa on 17/10/2014 10:19:58:

At the risk of going all "20th Century" on you …

.

Any 21st Century alternatives ?

Print one

Neil

[HopperParticipant @hopper]

Posted by Oompa Lumpa on 17/10/2014 10:19:58:

At the risk of going all "20th Century" on you, I wouldn't bother with all of the above (no disrespect) but I would simply make a new Leadscrew half nut using Delrin or similar and just heat the leadscrew up and crush the Delrin around it.

This I have found works well.

graham.

I have thought about that. Do little bits of swarf get stuck in the Delrin? Bit of a problem on the Drummond is the leadscrew is very exposed to swarf. which is why the original nuts wear out.

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