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View Full Version : Making new lead screws and nuts for a mill



daveo
01-07-2016, 02:18 PM
I have a old Wells 55 mill and one lead screw is wore out. The other is so so but I might as well replace it. The screws (acme 1.125 by 5) are pretty straight forward lathe work. But the nuts I have some questions... I could sleeve the existing nuts with new bronze sleeves and pin them in. Make new steel nut bodies and put a sleeve with bronze or plastic and pin them in. (or bolt them in)

I took me a hour and a half to get the mill apart and ready for new parts. Not something I want to do all the time. I have not ordered anything yet. Trying to decide what to do....

Toolguy
01-07-2016, 02:29 PM
Evanuts!:)

gcude
01-07-2016, 02:29 PM
Although I am a big fan of "EvaNuts", making one, or more specifically, removing one from 1.125" acme might be more than you bargain for. Probably should stay with bronze on this repair.

daveo
01-07-2016, 02:31 PM
Although I am a big fan of "EvaNuts", making one, or more specifically, removing one from 1.125" acme might be more than you bargain for. Probably should stay with bronze on this repair.


They make plastic nuts, but they are the same price as bronze!
I'm sure I could make a tap to do plastic out of a piece of scrap rod...

John Stevenson
01-07-2016, 02:49 PM
I have some questions... I could sleeve the existing nuts with new bronze sleeves and pin them in. Make new steel nut bodies and put a sleeve with bronze or plastic and pin them in. (or bolt them in)

I took me a hour and a half to get the mill apart and ready for new parts. Not something I want to do all the time. I have not ordered anything yet. Trying to decide what to do....

Did the exact same over Christmas on an Edgwick lathe as the nut was quite complex and I didn't have a lot of time.

http://www.stevenson-engineers.co.uk/files/edgwick%20screw2.jpg

Also did a spare nut whilst I was at it.

This one was 7/8" x 5 LH. Just a bloody good press fit and loctite

velocette
01-07-2016, 03:44 PM
Hi
Can I add my method to this pool and perhaps it can be used here.
Faced with the same problem on a smaller scale To replace a 15 x 1.25 pitch to a 16 x 2 mm pitch lead screws on an X2 Mill.
To attempt to have minimum backlash.
Cut the thread on the lead screw to finished size.
Then fabricate a tap from a harden able steel that is 0.1 mm oversize on the lead screw thread .
All done one one setting.
Bored the nut to the minimum thread depth on the lead screw
Cut the internal thread the same depth as the lead screw.
Then clean up the internal thread with the tap
Note!! the nut will be a good fit if turned 180 deg to match the profile of the lead screw.

Eric

daveo
01-07-2016, 04:21 PM
Wasnt that kind of tight? Screws do need some backlash to work...

Daveb
01-07-2016, 04:30 PM
The cost of Acme rod on your side of the pond makes me wonder why anyone would choose to make it. Am I missing something? TCT internal inserts are readily available in Acme profiles.
Just wondered, I have to do the same job, I bought the 1" X 5 Acme rod from the US, including postage about half the price I would have to pay here.

daveo
01-07-2016, 05:03 PM
Im buying the screws, 5ft for $91 bucks and a 2ft piece for $36. The bronze nuts are $109 for two...

But there is still a lot of lathe work to do to make them fit in the mill:D

daveo
01-07-2016, 05:51 PM
Did the exact same over Christmas on an Edgwick lathe as the nut was quite complex and I didn't have a lot of time.

http://www.stevenson-engineers.co.uk/files/edgwick%20screw2.jpg

Also did a spare nut whilst I was at it.

This one was 7/8" x 5 LH. Just a bloody good press fit and loctite


Awesome! The new bronze nuts are 2.500 in length. The originals are 1.750 in threaded length. Keep the 2.250 or cut them down?

steve45
01-10-2016, 11:11 PM
Have you priced new lead screws & nuts from Wells-Index? I'm sure they're not cheap, but they should be available.

Richard King
01-10-2016, 11:47 PM
If you need an easier way, next time check out http://www.greenbaymfgco.com

they make Acme screws and bronze nuts - on the shelf and cheap.

firbikrhd1
01-11-2016, 08:42 AM
Same problem on my Index Model 40. My solution was to order nuts and make holders to fit them.



http://i283.photobucket.com/albums/kk287/firbikrhd1/P5140045.jpg (http://s283.photobucket.com/user/firbikrhd1/media/P5140045.jpg.html)

http://i283.photobucket.com/albums/kk287/firbikrhd1/P5210053.jpg (http://s283.photobucket.com/user/firbikrhd1/media/P5210053.jpg.html)

Jaakko Fagerlund
01-11-2016, 09:24 AM
Fixed two manual mills and two manual lathes with new trapezoidal screw stock and bronze nuts. The nuts were turned down and a fine thread was made on the OD and the original nut was then modified to have that same thread not all the way through. A dap of Locktite, screw it in tight and it's as good as new :)

daveo
01-11-2016, 03:27 PM
Have you priced new lead screws & nuts from Wells-Index? I'm sure they're not cheap, but they should be available.

No, I dont have a problem making my own. I could use the experience anyway...;)

I am sending the spindle to Wells tomorrow to have it re-ground to R8. They have been helpful on getting it done via email..

J Tiers
01-11-2016, 04:27 PM
It's not too hard to make your own feedscrews. And you can likely get more accurate than the cheaper forms of pre-threaded, depending on how worn-out your lathe is. Some cheaper grades have considerable error, which will throw off your settings for longer movements.

Of course, you may HAVE to make your own if the size is odd, or there are other features on the screw, such as an integral gear, or full diameter unthreaded sections, etc, etc. In such a case, trying to add those features by some rigged-up splicing scheme may simply be more hassle than just making the part.

daveo
01-12-2016, 03:50 AM
It's not too hard to make your own feedscrews. And you can likely get more accurate than the cheaper forms of pre-threaded, depending on how worn-out your lathe is. Some cheaper grades have considerable error, which will throw off your settings for longer movements.

Of course, you may HAVE to make your own if the size is odd, or there are other features on the screw, such as an integral gear, or full diameter unthreaded sections, etc, etc. In such a case, trying to add those features by some rigged-up splicing scheme may simply be more hassle than just making the part.

1 1/8 by 5... One piece is almost 5 foot long. I will be buying it!



http://i297.photobucket.com/albums/mm234/daveo11/20160107_140819%20Medium.jpg

daveo
01-12-2016, 03:52 AM
Same problem on my Index Model 40. My solution was to order nuts and make holders to fit them.



http://i283.photobucket.com/albums/kk287/firbikrhd1/P5140045.jpg (http://s283.photobucket.com/user/firbikrhd1/media/P5140045.jpg.html)

http://i283.photobucket.com/albums/kk287/firbikrhd1/P5210053.jpg (http://s283.photobucket.com/user/firbikrhd1/media/P5210053.jpg.html)

Awesome!

dp
01-12-2016, 09:46 AM
One of a couple posts I've bookmarked from Practical Machinist.

http://www.practicalmachinist.com/vb/south-bend-lathes/making-new-cross-slide-acme-screw-150571/#post816663

It's good background information on how to make cutter and screw. If you can make a screw then it is a simple step to making a tap for a nut.

J Tiers
01-12-2016, 11:35 AM
1 1/8 by 5... One piece is almost 5 foot long. I will be buying it!



So you have a 4 foot table. Is the lathe long enough to work on the dial end details? If so, it's big enough to make the part if there are details that otherwise require splicing

Sunset Machine
01-12-2016, 11:41 AM
" One of a couple posts I've bookmarked from Practical Machinist"

Can I criticize his combined use of a three jaw and tailstock? He made a brand new bent screw by doing so.

MyrtleLake
01-12-2016, 12:50 PM
Over that long of a length, any bend would be incredibly slight. Very likely inconsequential for a leadscrew. That said, in reading through it later in the thread, he mentions that he is using a set-tru scroll chuck. He could have dialed it in very close.

I suspect you're advocating turning between centers, Sunset Machine? If so, wouldn't the fact the carriage is cutting away from the headstock likely cause problems there? It would be a tricky balance to apply enough tailstock pressure on a live center to overcome the cutting force but also not enough to slightly bend the stock from the axial pressure. Chatter would probably show up as well from the reduced support.

Lastly, if he cut the outboard center while the stock is mounted in the scroll chuck to begin with--then never touched the chuck until after the screw is cut--there should be no bend at all. Mounting stock through the headstock, drilling the center, then advancing and remounting the stock extended is where center offset would originate from. That is my understanding. Do you disagree?

daveo
01-12-2016, 01:54 PM
So you have a 4 foot table. Is the lathe long enough to work on the dial end details? If so, it's big enough to make the part if there are details that otherwise require splicing

The mill table is 46 inch. My lathe is only 36 inch...I was going to use a 4 jaw and a tailstock to do the ends of the screw. I only need machine a few inches on one end and 12 or so inches on the other. It all steps down, there are no big (bigger than the threads) shoulders on either end. Then mill a woodruff key in each end, and a square on one end. If I copy the originals...

I could graft the old ends onto the new screw but I was thinking, just turning the ends to suit would be a very acceptable (and better) repair... Am I wrong?

Sunset Machine
01-12-2016, 05:41 PM
Over that long of a length, any bend would be incredibly slight. Very likely inconsequential for a leadscrew. That said, in reading through it later in the thread, he mentions that he is using a set-tru scroll chuck. He could have dialed it in very close.

I suspect you're advocating turning between centers, Sunset Machine? If so, wouldn't the fact the carriage is cutting away from the headstock likely cause problems there? It would be a tricky balance to apply enough tailstock pressure on a live center to overcome the cutting force but also not enough to slightly bend the stock from the axial pressure. Chatter would probably show up as well from the reduced support.

Lastly, if he cut the outboard center while the stock is mounted in the scroll chuck to begin with--then never touched the chuck until after the screw is cut--there should be no bend at all. Mounting stock through the headstock, drilling the center, then advancing and remounting the stock extended is where center offset would originate from. That is my understanding. Do you disagree?

I see your points, but still. It's just bad practice. Sure, a guy could make a good one like that. But if he's that good, I think he wouldn't. One little oopsie and having to start over, or the next guy shaking his head as the leadscrew goes lop-de-lop. Why even start down that road? Just sayin.

Doc Nickel
01-12-2016, 05:53 PM
Why is it "bad practice"? By what mechanism would it produce a "bent" screw?

Doc.

Toolguy
01-12-2016, 05:55 PM
I am wondering the same thing.:confused:

John Stevenson
01-12-2016, 06:20 PM
At least he did it.

J Tiers
01-12-2016, 06:27 PM
I could graft the old ends onto the new screw but I was thinking, just turning the ends to suit would be a very acceptable (and better) repair... Am I wrong?

Not really, that's what I would do, I don't like grafted-together construction unless it is necessary. The problem comes in needing to hold the screw by the same portion you need to work on. If the headstock will swallow the screw right thru, then you have no problems other than supporting to outboard end.


Why is it "bad practice"? By what mechanism would it produce a "bent" screw?

Doc.

I expect he is thinking about the probable off-centered-ness of a three-jaw. That would put the chuck end off-center from the tailstock end, and the screw would rotate lopsided, because the machined parts of it would be off-center from the threads.

But if it was an adjust-tru, then he could get it as good as a 4 jaw.

daveo
01-12-2016, 06:43 PM
It will go thru the head stock. Im still trying to figure out how I will support the back end...

Mcgyver
01-12-2016, 06:54 PM
the issue isn't eccentricity imo, because he's turning the OD ....the issue is whether the three jaw is holding the work parallel to the lathe's axis or if its being forced over by the rotating centre.....if being forced over it its being turned with a spring in it.

Not sure i'd even consider it an issue, I guess it would depend on how much the centre was pulling it over. The reality is material stress will change its equilibrium and secondly the traveling steady will impose a reasonably consistent thread around whatever shape that equilibrium is, but do nothing to straighten it.

For really careful work you'd need to turn off the outer stressed layers or work with stress relieve material then careful hold it concentrically or between centres. I've done it that way, didn't do a side by side test so don't know if it made a difference....trying to get stuff on your side is an ongoing effort toward not getting bit

Mcgyver
01-12-2016, 06:58 PM
It will go thru the head stock. Im still trying to figure out how I will support the back end...

lathe spider

http://photos.yesterdaystractors.com/gallery/uptest/a131734.jpg

obviously be really careful with any length sicking out. you could just rest it on something if you go VERY slowly.....but too fast and it will get away from you in a split second and could be deadly

daveo
01-12-2016, 07:03 PM
lathe spider

http://photos.yesterdaystractors.com/gallery/uptest/a131734.jpg

obviously be really careful with any length sicking out. you could just rest it on something if you go VERY slowly.....but too fast and it will get away from you in a split second and could be deadly


I planed on that, but there may be 2 more feet sticking out past the spider....

John Stevenson
01-12-2016, 07:15 PM
Weld a bearing to a pole on a stand, plenty of weight on the bottom and you have a free standing steady.

J Tiers
01-12-2016, 09:55 PM
the issue isn't eccentricity imo, because he's turning the OD ....the issue is whether the three jaw is holding the work parallel to the lathe's axis or if its being forced over by the rotating centre.....if being forced over it its being turned with a spring in it.

Not sure i'd even consider it an issue, I guess it would depend on how much the centre was pulling it over. ......

It kinda IS about eccentricity though....

If chucked in something, even a collet, the reference surface for the workholder is necessarily going to be the thread OD.

So, if the workholding device is off-center, as a 3 jaw chuck always is, the turned surface of the bearing seat or journal is going to be non-concentric with the thread OD, which we will assume is concentric with the pitch line. (if it's not, then just hang it up, you are messed over to begin with). So when the thing is in its bearings, it will have a wobble.

That, in turn, can cause the nut to slide up and down the thread flank, and cause an irregular advance of the feed. If you move it "X" distance per the dial, it may be more or less than that distance, due to the wobble of the screw.

If it were for a lathe, that would result in more-or-less drunken threads when the resulting screw was used to cut threads.

Will it be a lot? That depends on the eccentricity, the rigidity of the halfnuts and so forth. If the thing is old and sloppy, it may not be the worst problem the thing has.

If. on the other hand, you use the centers, you are using the reference that was used to cut/mill/grind the threads. Now you should end up right on the center, and cannot have the problems as expressed above.

MyrtleLake
01-12-2016, 10:54 PM
I do not believe eccentricity has any issue here.

"...the first photo shows me cutting the gear diameter on the screw on the lathe. I didn't remove the part from the lathe after cutting the acme threads and it's still in the original set up." post #23 (http://www.practicalmachinist.com/vb/south-bend-lathes/making-new-cross-slide-acme-screw-150571/index2.html#post819662)

"I needed to work on handle end of the screw. I mounted the screw in a set-tru type chuck and using a dial indicator adjusted the run-out to none (0)." post #33 (http://www.practicalmachinist.com/vb/south-bend-lathes/making-new-cross-slide-acme-screw-150571/index2.html#post821640)

He is indicating off of a section (where the gear is cut) that was turned at the same time / set-up as the thread itself. The only possible issue I see is a pre-drilled center being pulled over by the tailstock center if not drilled in one set-up. It is a very minor point, I feel, over the full length of a leadscrew. IMO, it is worth a theoretical note but not a practical critique. John Stevenson's post is more poignant: he did a good job :)

J Tiers
01-12-2016, 11:22 PM
I do not believe eccentricity has any issue here.
...
He is indicating off of a section (where the gear is cut) that was turned at the same time / set-up as the thread itself. The only possible issue I see is a pre-drilled center being pulled over by the tailstock center if not drilled in one set-up. It is a very minor point, I feel, over the full length of a leadscrew. IMO, it is worth a theoretical note but not a practical critique. John Stevenson's post is more poignant: he did a good job :)

IN THAT CASE, no it doesn't, but that is ONLY because the entire thing including threads is cut in one setup, per your quote. Even your quibble is a non-issue so long as the threads were cut using the center in question.

THAT DOES NOT APPLY in the case of a screw which arrives pre-threaded, and is to be machined on the ends. In THAT case it is best to use the same references that were used to cut the threads, which are presumably the centers.

If the chuck is used, as the OP here proposes to do (he CANNOT do it between centers), then you are totally dependent on two things: First, that the thread OD is concentric with the pitch line, and second, that the chuck will not contribute any eccentricity, or is capable of adjusting out any that exists.

A 4 jaw, or adjust-tru, will adjust out eccentricity, but you next need a reference for centering. That should be the center hole in the part. So you would need to adjust to bring the center in the end being worked on to zero runout.

Probably it would be best to stick out only a minimal amount, adjust, and do the end-most diameter first, so as to have a good OD reference for later. Or you could assume an even amount of OD runout as manufactured. Then you could stick the end out as far as needed, put it in a T/S center, and then adjust the chuck to have an even amount of runout all along from chuck to center.

If you do manage to get the bearing journals out of concentricity with the pitch line "cylinder", you will have the wobble and potential problems I mentioned. But it's reasonably easy to avoid that, so long as you use a chuck that either is accurate (collet) or that allows a centering adjustment (4 jaw, adjust-tru).

Richard King
01-15-2016, 09:02 AM
I have to say I didn't read the whole thread. Amazing what is on You tube nowadays. I enjoy Tom advice. https://www.youtube.com/watch?v=w46cnvjIJzA

bborr01
01-15-2016, 10:57 AM
Really? Sounds like someone needs a new chuck.

Brian




So, if the workholding device is off-center, as a 3 jaw chuck always is,

MyrtleLake
01-15-2016, 12:57 PM
Really? Sounds like someone needs a new chuck.
"This type of chuck [self-centering scroll chuck] will usually center work within 0.003 in. when new, but when the scroll becomes worn, this degree of accuracy cannot be expected. Since there is no way to adjust the jaws independently, this chuck is not used where extreme accuracy is required." p371 Machine Tool Operation Vol. 1. Burghardt & Axelrod.

"Because of the clearances required to allow this mechanism [the scroll] to operate without binding and because of wear, three-jaw chucks do not always hold the workpiece accurately in terms of a few thousandths of an inch. In many cases this is good enough; however, when greater accuracy is required..." p253 Machine Shop Practice Vol. 1. Moltrecht.

"Round and hexagonal work may be chucked quickly in the universal chuck as all three jaws move simultaneously and automatically center the work within a few thousands of an inch. This type of chuck will usually center work within 0.003 in. when new, but when the scroll becomes worn this degree of accuracy cannot be expected. Since there is no way to adjust the jaws independently on this type of chuck, it is not used where extreme accuracy is required." p56 How to Run a Lathe. 1942 Ed. South Bend Lathe Works.

"Just as most model engineers expect their lathe to do work far in excess of that for which it was designed, so they seem to expect quite unreasonable degrees of accuracy from their chucks! The main purpose of the self-centering chuck is to hold round or hexagonal stock reasonably true with the minimum of effort. It is a 'tool of convenience'. The 'normal' workpiece envisaged was one which would be finished and parted off at one setting but which was too short to hold between centres. Some pieces might have unmachined parts -- hexagon bolts, for example -- but in this case a slight eccentricity of the unmachined part would not matter. In normal manufacturing neither the Designer nor the Production Engineer would expect to reverse the work in the chuck -- apart, perhaps, for a simple end-facing operation; and even this would normally be carried out on a 'second operation' machine...

"All chucks are made to tolerances... the guaranteed concentricity of a standard 4 in. chuck is no better than about 3 thousandths of an inch T.I.R. (Total Indicator Reading.) The repeatability will be better than this -- that is, the change in T.I.R. on stock of the same diameter is usually better than 0.0015 inch. But if the workpiece is turned about, and held at a different chuck jaw setting, then you may well be finding your D.T.I. indicating a total runout of more than 3 thou, even on a new chuck perfectly acceptable to British Standard No. 1983." p62 Workholding in the Lathe. Tubal Cain.

daveo
01-15-2016, 01:31 PM
I have a brand new 3 jaw Bison that wont center work perfectly... This is why they make 4 jaw chucks or 3 jaw independent chucks...

Richard King
01-15-2016, 04:00 PM
Isn't a Bison made in China? Not a big surprise it is junk.

Toolguy
01-15-2016, 05:27 PM
I think Bison is made in Poland. I have a 6" 6 jaw Bison chuck that is still very accurate after years of almost daily use. It is a set-true style, but is within a couple thou or better through the range of different diameters. It is my favorite chuck.

MyrtleLake
01-15-2016, 05:39 PM
Bison-Bial (http://www.bison-bial.com). Polish. Very accurate and well made chucks. Tolerances (http://www.bison-bial.com/public/data/resource/upload/00198/197495/technical-data-de.pdf).

daveo
01-15-2016, 07:48 PM
Isn't a Bison made in China? Not a big surprise it is junk.


LOL... Some of the best chucks made...