Metric feedscrews for ML7 /S7

[Martin DowingParticipant @martindowing58466]

I got damaged metric feedscrew for Myford ML7.

It looks like it is 3/8 inch diameter 2mm pitch 29deg ACME screw.

Am I correct?

It looks like this screw is of mixed metric – imperial design.

Does such a screw exist at all in standart engineering charts?

[Martin DowingParticipant @martindowing58466]

Metric feedscrews for ML7 / S7

[DC31kParticipant @dc31k]

Posted by Martin Dowing on 02/03/2021 00:24:50:

It looks like this screw is of mixed metric – imperial design.

Does such a screw exist at all in standard engineering charts?

Second question first: no. Another question: why do you think it should do so?

First statement: highly likely.

Put yourself in the shoes (left shoe size 9, right shoe size 228.6) of the manufacturer with a mixed metric and imperial inventory.

Consider what is easiest for your leadscrew cutting department.

Keep one size of stock in your stores. Have a bar feeder that is set up for that one size of stock. Grind tools to one angle. Flip a lever that changes the cut pitch from say 1/4" to 6mm.

Keep both metric and imperial stock in your stores. Make sure the correct one is issued when called for. Change over the bar feeder on the leadscrew machine when a different language is required. Tool grinding department now has two types of tool to make, stock, and issue.

You might do the same mental exercise on the halfnuts that mesh with the leadscrew and see the considerable advantages of minimising the differences between imperial and metric versions. Same with leadscrew support bearings.

[not done it yetParticipant @notdoneityet]

First thing is to actually measure it. Then you will know whether you are correct, or not. ‘Looks’ can be deceiving. Are you sure it is not 10mm (can you tell 1/2 a mm by looking)? Are you sure it is not cut at 30 degrees (can you tell the difference between 29 and 30degrees)?

DC31K is spot on. What graduations are there for this feed screw? Factory or home-made?

If it is of mixed metric/imperial dimensions, you would need a non-standard chart, methinks.

[HopperParticipant @hopper]

So this is the cross slide feed screw?

Sounds like a Myford special made as a cost saving measure on their imperial thread roller fitted with metric rollers,  if it is in fact 3/8 diameter and 2mm pitch. If so you have three choices:

1. Buy new Myford parts, if / when available — at the Myford price.

2. Substitute some 10mm x 2mm pitch trapezoidal threaded bar and matching nut which is readily available but will need machining to suit the Myford handle and dial and the nut will need modding too. Or make your own nut using tap from Tracy Tools etc.

3. Repair the existing damaged screw, which you have not described in detail. The usual dodge is to cut the handle end off the screw, flip the threaded section around 180 degrees and attach handle to the other end. Usually done by drilling and reaming a hole in the ends of each piece and inserting a pin to join the two pieces, which is then silver soldered, loctited or pinned in position.

Edited By Hopper on 02/03/2021 07:59:15

[Martin DowingParticipant @martindowing58466]

@not done it yet,

Measured indeed.

3/8 inch for certain, angle is still not 100% certain but rather 29 than 30 deg.

@DC31k,

Thanks for these comments – they make good sense.

[Martin DowingParticipant @martindowing58466]

Posted by Hopper on 02/03/2021 07:58:10:

So this is the cross slide feed screw?

Sounds like a Myford special made as a cost saving measure on their imperial thread roller fitted with metric rollers, if it is in fact 3/8 diameter and 2mm pitch. If so you have three choices:

1. Buy new Myford parts, if / when available — at the Myford price.

2. Substitute some 10mm x 2mm pitch trapezoidal threaded bar and matching nut which is readily available but will need machining to suit the Myford handle and dial and the nut will need modding too. Or make your own nut using tap from Tracy Tools etc.

3. Repair the existing damaged screw, which you have not described in detail. The usual dodge is to cut the handle end off the screw, flip the threaded section around 180 degrees and attach handle to the other end. Usually done by drilling and reaming a hole in the ends of each piece and inserting a pin to join the two pieces, which is then silver soldered, loctited or pinned in position.

Edited By Hopper on 02/03/2021 07:59:15

I have such metric screws on my machine for a long time and there are no issues with them.

When I made an upgrade to long cross slide and "modern" looking top slide long time ago I got it all in metric forms.

However my friend brought to me damaged (bent) metric feedscrew from his topslide and asked me to make duplicate.

Then I have started measuring and found something weird – mixed metric – imperial design.

Myford sells them but they are calling close to 1000 quids on ebay (!!!) and anyway "new Myford" stuff usually is not really a match for original parts.

Once I have ordered myself replacement tailstock barrel and it came with badly scored 2MT socket, damaged as new.

After complaining they replaced it but meantime I have made one myself, even better in quality than what they sent and also made of 45 HRC material but with only short section of ACME thread – suitable for lever operated tailstock.

[JasonBModerator @jasonb]

The high e-bay price is because they don't have any in stock, just saves relisting the item

[John HaineParticipant @johnhaine32865]

How did you measure it? 3/8" = 9.525 mm, 9.5mm = .374 in.

[Martin DowingParticipant @martindowing58466]

Posted by John Haine on 02/03/2021 08:50:50:

How did you measure it? 3/8" = 9.525 mm, 9.5mm = .374 in.

With micrometer (Starrett 0-25mm), across threaded section.

Result: 9.56mm

Edit:

@Jason,

Thanks for this comment but I would not take a risk to test click it to find out for sure.

I bet they would find one facing such opportunity.

Edited By Martin Dowing on 02/03/2021 09:27:53

[John HaineParticipant @johnhaine32865]

Well, that indicates that it is more likely to be made to a nominal metric diameter surely?

[Martin DowingParticipant @martindowing58466]

Posted by John Haine on 02/03/2021 10:16:02:

Well, that indicates that it is more likely to be made to a nominal metric diameter surely?

At 9.8mm you would have a point, but at 9.56 – unlikely.

I have an original imperial 3/8 inch / 20TPI ACME feedscrew made by Myford (Nottingham). It has diameter exactly 9.52 mm.

Applying your logic it should have diameter 9 – 9.1 mm.

[John HaineParticipant @johnhaine32865]

A nominal 9.5 mm which is +.02 either due to manufacturing or measurement tolerance. The usual metric nearest to 3/8 is 9.5 mm (3/4 being 19 mm).

[HopperParticipant @hopper]

Posted by Martin Dowing on 02/03/2021 08:38:07:

However my friend brought to me damaged (bent) metric feedscrew from his topslide and asked me to make duplicate.

From scratch, cutting your own thread, or using bought-in threaded rod? If the former, easy enough following the dimensions of the original and screwcut in the lathe with a travelling steady. Mixed dimensions don't matter if you just copy them. If the latter, buying in threaded rod, then you will have to go fully metric and arrange matching nut.

Personally, I would be looking hard at straightening the bent feed screw. Usually they get bent on the plain section where the handle and dial fit on so not too hard to get straight again, or cut the plain section off and make a new one and graft it on with a spigot. If the threaded section is bent, the core diameter is so small it should not be too hard to get it straight again with a bit of care. Heavy vice or light press should do the job or even a leather mallet on a block of wood, depending on how bad and where it is bent.

[Martin DowingParticipant @martindowing58466]

@Hopper,

I will rather need to cut it.

It is bent across threaded section and badly.

He dropped something heavy on it.

I will only need to find a way to find if it is 29 or 30 degree angle.

@John Haine,

Standard metric sizes of trapezoid screws are 8 and 10 mm @ 30 deg.

[HopperParticipant @hopper]

Knowing Myford, they most likely used a standard Acme profile, just like they used a standard imperial diameter, so it would be 29 degrees.

You might be able to press some plasticene or putty into the thread then pull it out and cut a cross section and meausure the angle under a magnifier. Otherwise, grind your thread cutting tool to match the thread profile on the old screw. The end sections should be unworn and make a handy gauge.

Half a degree difference in each flank angle going into a worn nut is probably a bit moot anyway.

Edited By Hopper on 02/03/2021 12:02:40

[Howard LewisParticipant @howardlewis46836]

My guess is the same as Hopper's.

Myford will have used standard Imperial material for the Leadscrew, (Otherwise they would make everything that engages with it to Metric dimensions.. This would entail extra costs in inventory and tooling, so non preferred.

So a hybrid with Imperial dimensions apart from a Metric pitch so that the minimum number of non Imperial parts have to be made from stock size material, and stocked. Possibly only the matching nut and the Dial

I would have expected Myford to use the minimum number of Metric dimensioned components on the machine.

The greater the variety of sizes, the greater the risk of confusion resulting in incorrect components being fitted or supplied. I have seen it happen!

Hybrid gets my vote.

Howard

[John HaineParticipant @johnhaine32865]

Posted by Martin Dowing on 02/03/2021 11:41:49:

 

@John Haine,

Standard metric sizes of trapezoid screws are 8 and 10 mm @ 30 deg.

Standard? This is Myford! The metric S7 has an 8 tpi leadscrew!

Just to confuse the issue my topslide feedscrew is 0.373" by my imperial mic which is 9.474mm! I also have a spare metric cross slide screw which I think is an ML7 one, 2mm pitch by about 270mm long. It measures near enough 9.5mm or slightly less depending on where you measure it. I bought it a long time back as a replacement for a very badly worn Aciera F1 screw but I sold the machine before getting round to fixing it.

Somewhere I also have a mating nut.

Martin, I just sent you a PM.

Edited By John Haine on 02/03/2021 17:25:46

[HopperParticipant @hopper]

Posted by John Haine on 02/03/2021 17:22:43:

Posted by Martin Dowing on 02/03/2021 11:41:49:

@John Haine,

Standard metric sizes of trapezoid screws are 8 and 10 mm @ 30 deg.

Standard? This is Myford! The metric S7 has an 8 tpi leadscrew!

Just to confuse the issue my topslide feedscrew is 0.373"

Which is normal for a nominal 3/8" thread. Needs to be tip clearance between male and female threads so they don't bind. If I were making it myself, I would go a bit further and make the OD of a 3/8 thread about .370".

[JasonBModerator @jasonb]

Or you could just buy one from here complete with bronze nut at a reasonable price.

[Author]

Posts