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Myford VMC Mill new nuts

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Ian Skeldon 209/06/2021 18:35:35
540 forum posts
54 photos

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I stripped the mill a while back and noted that although the lead screws were in great condition, the nuts had done a lot of work and had a fair bit of wear evident.

So after reading about Kennions being excellent suppliers of stock I ordered 2 x 66mm dia bar to make my two new nuts. i ordered the bar on Tuesday and it arrived on Wednesday morning cut perfectly to size and extremely well packaged. I will certainly use this supplier again.

Anyway I promised Nigel Graham I would update anything I did with my mill as he has the same mill and is interested to see what I do.

So today I made a start, First piece into the lathe, trued up and then turned in the same way that you would make a cube. Photo's below.

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Edited By Ian Skeldon 2 on 09/06/2021 18:36:13

Ian Skeldon 209/06/2021 18:41:41
540 forum posts
54 photos

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old mart09/06/2021 19:39:48
3316 forum posts
203 photos

What spec bronze are you using for the nuts? I have made them from leaded gunmetal SAE660.

Ian Skeldon 209/06/2021 22:25:00
540 forum posts
54 photos

Hi OM,

I am using the same spec as you used SAE 660.

It cuts really well and should prove to serve the purpose for the rest of my life time. Only problem I can see at the moment is cutting the thread. I have searched the internet pretty hard and can't find 1" 5tpi ACME inserts for a tool that will fit into the bore. I only have a basic bench grinder so grinding something accurately is going to be challenging, mmm I might look for a tap although I guess they either don't exist in that spec or they cost as much as a mortgage!

ega09/06/2021 22:44:10
2242 forum posts
186 photos

Ian Skeldon 2:

I could let you have an insert marked "5 ACME GC10F" if you think it will do your job.

PM me if you want to pursue this,

Edited By ega on 09/06/2021 22:45:42

Nigel Graham 209/06/2021 23:30:12
1676 forum posts
20 photos

Thank you for the promise, Ian!

And interesting progress report.

Tracy Tools list ACME taps up to 3/4" . £40. They say other sizes are available but, no, they won't be cheap.

I've still the problem with my mill of the very stiff quill, so much so that sensitive drilling is a gamble. Unfortunately I can't see how to gain access to the rack and pinion, which might simply be bunged up with congealed grease, and I don't have the tools for handling the spring safely.

There's also a curiou spot on the long travel where the handwheel seems to suddenly jump ahead of itself, but I have not been able to establish exactly where and in what circumstanes this happens.

William Chitham10/06/2021 11:38:01
122 forum posts
49 photos
Posted by Ian Skeldon 2 on 09/06/2021 22:25:00:

problem I can see at the moment is cutting the thread. I have searched the internet pretty hard and can't find 1" 5tpi ACME inserts for a tool that will fit into the bore. I only have a basic bench grinder so grinding something accurately is going to be challenging, mmm I might look for a tap although I guess they either don't exist in that spec or they cost as much as a mortgage!

I've just run into the same problem, can't get a big enough insert to cut a 7tpi BSW thread to fit my 16mm holder. A pre ground HSS tool solves my problem but don't suppose they are available for ACME profiles. To make one from scratch how about starting with a good size bar of silver steel and turn the thread profile on the end, instead of grinding. Then use the grinder to establish a cutting edge and reliefs and finally harden and hone. Hope this horrible sketch communicates the idea, not new I am sure.

William.

20210610_112720.jpg

old mart10/06/2021 17:35:42
3316 forum posts
203 photos

Funny you should mention 1" x 5 ACME, I have just made a tool to hold the er22 5tpi Acme lay down insert. The tool will pass into the 0.800" start bore for that size. You will never be able to buy one as tooling for that size would need a start hole more than 1 1/4 " diameter. The tool is right hand and will be used away from the chuck for a LH thread. I will have to measure the working length, maybe 2 1/2". The knee of the Tom Senior could do with a new nut.

I would be willing to lend you the tool, if your lathe can manage it.

 

 

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Edited By old mart on 10/06/2021 17:38:12

Edited By old mart on 10/06/2021 17:39:31

Ian Skeldon 210/06/2021 21:38:35
540 forum posts
54 photos

Ega and Old Mart, thank you so much for your very generous offer. Personally I am reluctant to let others use my tools for fear of misuse or damage, the fear that I may damage or even destroy your tools is the reason that I will decline your kind offer and sincerely hope that this does not offend you.

I agree with Old Mart about the size of tooling being to big to pass through the bore. I think bot William and Old Mart have the right approach in so much as I need to make a tool to do the job, I am not sure which way to go, grind some hss into the required profile or make a holder and use a home made hss insert. In fact I have just had a thought, maybe I could buy a hss boring tool and regrind that to the required profile?

Nigel, i took my spring cover off and the spring sits neatly inside it, I made a simple tool using a piece of square bar, drilled two holes in it and put pegs in it to re-tension the spring upon re-assembly. If I can find it I will photograph it and pass on the details.

Thank you again Ega and Old Mart for your offer.

Ian

Nigel Graham 210/06/2021 22:46:52
1676 forum posts
20 photos

You could grind an HSS boring-tool, alterntively use the steel-insert type boring-bar in which the cutting tip itself is a small piece of HSS round.

As it happens this is a problem I have to solve for myself, not for a machine-tool but the steering-gear for my steam-wagon. I have worked out it should be a long-lead so 2-start thread, square or ACME - probably 3/4" dia X 1/4" lead - to give about 4 steering-wheel turns lock-to-lock. My thought is either a steel-insert boring-bar, or to turn what is effectively a single-tooth tap in silver-steel.

For the latter, screw-cut enough of the silver-steel to pass right through the nut, then either machine grooves in it to create a machine-tap that will be driven by the change-wheel train, or neck the material behind the last turn down to leave just a single cutting-tooth.

'

Just a thought... there are internal tools that use a circular insert screwed onto the end face of the boring-bar. These are typically for cutting O-ring and circlip grooves, but I wonder if there are thread-cutters made for these. If so ones of appropriate size may be available.

I looked on the Cutwel (one 'L' ) site, and though they do stock such tools they do not include ACME cutters. They do though sell the more conventional flat-mounted inserts and holders for ACME internal threads.. .but apparently not 5TPI

'

Thank you for the offer! Yes, if you can find it I will appreciate it. I am very wary of clock-type springs, from near-misses many years ago and warnings published for those making clocks - and using special tools for that.

From what I can see, one end of the quill spring is clipped into the cover, the other to the shaft, but I can't see how in detail, nor how to release all the tension safely. I don 't think simply unwinding the cover is enough to slacken it fully.

Edited By Nigel Graham 2 on 10/06/2021 22:53:46

duncan webster11/06/2021 00:40:29
3456 forum posts
63 photos

You can buy ready made acme nuts This is from USA Acme and costs $41, I'm sure you can get them in UK. Cheaper than buying a tap.

William Chitham11/06/2021 09:50:04
122 forum posts
49 photos
Posted by old mart on 10/06/2021 17:35:42:

Funny you should mention 1" x 5 ACME, I have just made a tool to hold the er22 5tpi Acme lay down insert. The tool will pass into the 0.800" start bore for that size.

Looks like a lovely job, is that made from silver steel, will you harden it? I'm a bit hazy about insert codes but does er22 denote an external thread insert intended for a 22mm bar, if so why not an internal NR type?

William.

Nigel Graham 211/06/2021 13:03:58
1676 forum posts
20 photos

Duncan -

Thank you for that lead (oh dear!).

I've not yet found ACME-thread suppliers at reasonable cost in the UK. One that seems home-buyer friendly, is Accu, stocking trapezoidal lead-screw lengths and nuts at very reasonable prices which may suit my, and others', applications though not here, as they are metric.

The advantage is that of buying matched components.

There are companies supplying ACME parts but most appear to be manufacturers working to trade orders, and priced accordingly.

old mart11/06/2021 18:39:51
3316 forum posts
203 photos

I had a bit of a snigger when I read the comments about the tool I had made to hold the 22 size insert and still pass into a hole of 0.800". I have to confess two points regarding that tool. It is made of a bit of steel that was laying around, and I strongly suspect it is a bit of stainless steel. The photo is the only one taken of it and as soon as I fitted the insert, I realised my mistake. The insert housing is much too near the end of the tool and the insert overhangs the end dangerously. The entire end has now been remachined to give the best support that I could manage.

Regarding lending the tool, The chance of damaging it is remote if careful attention to the actual thread cutting is adhered to. With a 5 ACME, the actual depth of thread is 0.1" deep from the start bore of 0.8", resulting in a finished diameter of 1". This might have to be increased very slightly if the leadscrew is used as the go gauge.

To use the leadscrew as a gauge, you would have to remove the tailstock.

If the thread is produced in multiple passes normally, from first touch in the bore, depths of +0.015",(twice) + 0.014", +0.012", +0.010", +0.008", +0.006", +0.005",(twice) +0.004, +0.003", +0.002", +0.001", which make the total 0.1" deep cut. Any further passes to get the leadscrew just fitting to be made at 0.001" or less. The reduction in depth of cut as the threading gets deeper is because the ammount cut is getting bigger each time.

I can make another tool any time and your only requirement would be to buy me another insert if you broke it which is very unlikely, so the offer stands.

I'm back at the museum tommorrow and will be able to measure the working length of the tool, which will have to be longer than your nuts if the thread is right hand to give you time to disengage the leadscrew nuts after each pass.

Edited By old mart on 11/06/2021 18:49:30

Ian Skeldon 212/06/2021 16:51:44
540 forum posts
54 photos

Hi Duncan, I will take a further look at the possibility of a UK Nut, even one from USA if I must.

But I will very gratefully accept Old Marts kind offer and PM him.

Nigel I am a bit busy working shifts at the hospital at the moment but will send you details maybe even the tool itself and a quick you tube showing what to look for and do.

In the mean time, thank you to everyone for their ideas and offers of help.

Best regards,

Ian

old mart12/06/2021 19:14:04
3316 forum posts
203 photos

I remembered to check out the ACME threading bar when I was at the museum today, and have brought it home with me.

After a bit of a struggle, I managed to find your address and the tool will be in the post Monday.

If you are careful and take the cuts that I recommended in my post of the 11th, there is no danger of a crash. The hard thing I find is remembering to go back to the zero on the cross slide every time before withdrawing the tool. It helps to have the settings on a piece of paper and tick them off as you go. I would try out the leadscrew for fit during the last few cuts.

 

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Edited By old mart on 12/06/2021 19:16:02

Edited By old mart on 12/06/2021 19:23:25

Edited By old mart on 12/06/2021 19:30:38

Nigel Graham 212/06/2021 22:07:24
1676 forum posts
20 photos

I received a tip from two fellow club-members today who have both bought components from -

- HPC Gears.

Yes, looking on its web-site, they list both metric and imperial lead-screws and nuts.

old mart12/06/2021 22:52:02
3316 forum posts
203 photos

Those figures I put down would be easier to manage in a slightly different form. Starting by just touching in the 0.800" bore and setting 100 on the cross slide, using thousandths of an inch numbers and working back towards zero.

100 - 85 - 70 - 57 - 47 - 39 - 32 - 26 - 21 - 16 - 12 - 9 - 6 - 4 - 3 - 2 - 1

Start checking the fit at 3. There is a possibility that you might reach 1 and still not be able to get the leadscrew to go in. You would have to creep up slowly in that case. Also worth checking if things were tighter than expected, would be the core diameter of the male thread. I have machined this gunmetal dry, and if you have an airline, blow the swarf out every pass.

Ian Skeldon 216/06/2021 15:47:46
540 forum posts
54 photos

Hi OM,

The tool arrived today, it's very impressive, I am not sure how you milled out the tool seat? maybe that could be an item or topic for Neil to publish?

I will hopefully take some photos as I go along, Once again many thanks.

Ian

old mart16/06/2021 18:27:13
3316 forum posts
203 photos

Glad you have got it, now for some very careful setting up. I would shim the tip height about 0.005" above centre. I hope the tool is long enough for you to comfortably disengage the nuts, I made it just long enough for the nut length I wanted, but I have the easier left hand threading away from the chuck. I have relieved the lower part of the insert because the helix angle is greater with that small diameter to pitch ratio. If you need to turn the insert, you shouild also use a diamond file to relieve the lower edges of the next edge. There is very little chance of blunting the insert cutting bronze. Make as many nuts as you like. You could even produce a test nut made from a bit of aluminium, if you do, use WD40 or equivalent to lubricate things.

I have checked out HPC gears and have bookmarked them in my favorites, they could be very useful.

Edited By old mart on 16/06/2021 18:31:11

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