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Myford ML7 1950 vintage

Proposed salvage of tailstock handwheel ACME thread

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Stefan Green28/08/2020 17:55:40
1 forum posts

Hello

I have been a member for some time but have never used the Forum. I live 10 miles south of Derby. My workshop is a 15x8ft single brick extension to my garage which I built in 1982 in anticipation of retirement; that occurred in 2002 as a result of 9/11. My hobby has turned out to be machine accuracy in resurrecting small machines, completing a part-finished Dore-Westbury Mk2, and making tooling. As well as the Myford I have an Utting power hacksaw, a Dowling engraver, a Stent hybrid T&CG (Stent base/Quorn-type Hoffman wheelhead) which featured in MEW220 in a 4-facet drill grinding article. All of these machines were disposed of as (or turned out to be!) scrap. The D-W needed corrective work as well as finishing due to the x-y saddle factory machined right-angle having been altered, and the R8 spindle taper being machined incorrectly. With this stable of machines, I am quite often a one-man Repair Shop.

I was hoping that there would already have been some discussion/information about the ML7 tailstock handwheel ACME threads, but I have been unable to find anything relevant neither on this forum nor Practical Machinist. So here goes . . .

During Lockdown I have been tackling some long-standing problems on my 1950 Myford ML7. One of its problems is that the 1 inch Acme left-hand thread in the cast iron tail stock handwheel is very worn - probably 40% non-existent & the rest is very sloppy. Most of this wear occurred during the 20 years industrial service before the machine was scrapped off. And yet, ironically, the bed is well within the Myford limits for needing a regrind. And I can turn anything to 1 thou TIR over 16 inches & tailstock ream to 2-3 tenths TIR.

I have made a carbide screwthreading turning tool out of a scrap solid carbide milling cutter, and have produced a trial threaded boss in aluminium. I have then shaped this into a suitable cone & fastened it onto the tailstock handwheel using a profiled ring with 4 thin capscrews; the spokes of the existing handwheel are then clamped between the ring and the boss without making holes in the spokes. This enables a small timing adjustment to be made in order to align the 2 sections of thread. The result is amazingly smooth.

However I would like to salvage the handwheel in order to provide a decent thread throughout the traversing range, but I cannot find any online reports anywhere that this salvage has ever been attempted.

I have spent a lot of time doing the stress calculations in order to work out whether a sleeve inserted into the bored-out handwheel would result in any problems with the thrust plate groove failing from the drilling force of doing a very large diameter drilling op e.g. 1.1inch dia which is my largest drill.

My salvage design thoughts are to produce 2 phosphor bronze sleeves threaded to the correct size. I will use one to produce a slave handwheel from a large piece of very rusty cast iron (shaped like a casting for a Myford drive plate, only bigger) which I happen to have. But it unfortunately has a rusty bore in it which is stepped from ~1.14 inch in diameter at the boss end down to 0.75inch at the 6inch dia face.Therefore the metal thickness between the bottom of the thrust plate groove and the oversized bore will end up on the skinny side – if I’m lucky 0.100inch; unlucky it will be around 0.70inch. And the sleeve will be pretty thin too. But it will give me an idea of whether modifying the actual handwheel is a good one or not. It will also give me a functioning tailstock while modifying the ML7 handwheel. If it looks as though it will work, I will either repeat the process on the actual handwheel, using the second sleeve, when I hope to end up with a slightly larger section under the thrust plate groove. Or I will call it a day and either live with my current lash-up or tidy the interim design to look similar to the Super7 solid handwheel – but with thrust plate screw access hole and painted, not chromed.

Has anyone ever done a successful salvage along these lines? Or a different method perhaps? I would like to hear from you even if you have tried and failed - but especially if you have tried and succeeded!

I look forward to any feedback. It's a great shame that there does not seem to be a single one of the ML7 resettable replacement handwheels around - only the Super7 version.

Out of interest, suitable left-hand ACME threaded sleeves are available in the US, but export taxes are prohibitive – the quotes I have had are from $120 to $140 each for a listed price of $15!!!

Stefan Green

Andy Carlson28/08/2020 22:27:20
431 forum posts
132 photos

Welcome to the forum Stefan. Sorry I don't think I can offer anything beyond moral support but it sounds like you have done your homework. I'm currently working on making a new cross slide nut insert for my Faircut - 12 TPI 3/8 inch square threaded. It's proving to be a bit of a challenge.

Hopper28/08/2020 23:02:46
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6220 forum posts
322 photos

Welcome aboard.

I can't visualise it without pics. But it sounds like you need to turn up a complete new hub then bore the handwheel out to fit and Loctite and pin them together.

Going by very rusty memory you may have to make the hub OD stepped and cut off the leading section of the old handwheel. The new hub would contain both the internal thread and external retaining groove in one piece. So all she loading from forces of drilling and the retainer plate are borne by the new hub. The only force on the old handwheel is your hand pressure rotating it.

E

Edited By Hopper on 28/08/2020 23:17:54

David George 129/08/2020 07:56:09
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1811 forum posts
503 photos

Hi Stefan welcome to the forum. I have a Myford M Type and have made a cross slide nut recently, which is a lot smaller diamiter,to repair the thread and made my own screw cutting tool from a piece of HSS. I don't think you should have any problem making a new boss for the handwheel complete with retaining groove. Just Locktite and drill and pin on the joint line between the new and old parts.

20190520_080901.jpg

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David

Stub Mandrel04/09/2020 19:06:22
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4315 forum posts
291 photos
1 articles

Welcome Stefan,

My recollection is that such handwheel repairs have been covered in ME and MEW a few times over the years, cutting square threads certainly has, although it sounds like you have a strategy to address the problem.

Neil

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