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advice on how to male a new cross slide leadscrew and nut for it

woodfarmer

Plastic
Joined
Nov 11, 2014
Hi
My 95 year old Holbrook is beginning to show some signs of wear in the cross slide. The leadscrew is worn in the centre part and also the nut has a little bit of wear. Currently the thread employed is 8tpi square, The nut seems to be made of brass.
Looking at it I thought the leadscrew was 1/2 inch diameter but it is in fact 0.556 inch. This has foxed me and I cannot see any reason why 1/2" was not used.
I originally thought to use a 10 TPI Acme tap to make a new nut and acme lathe tool for the leadscrew thread, switching to 10 TPI would reduce the feed a little and if I were to use a 100 segment handwheel would maybe be simpler. I doubt I will find a tap of .556 inch diameter.
Is there any reason I shouldn't use 1/2" ?
I wont need for it to last for another 95 years so am quite willing to use an easy to machine steel for the leadscrew and anything easy for the nut, posssibly even plastic. Five years of light use will be enough for me.
the leadscrew fits into the lathe through a hole and after the screw part (and a bit of unthreaded bar) emerges under the toolpost the only thing it touches is the nut.
so two questions : What would be suitable materials and is there any reason not to use 1/2 inch for the screw thread and nut ?

Thanks for your help
 
If the lathe isnt worth much,and you want a cheap fix,use the screw and nut from a cheap car jack,scissor type...........Ive used these many times in small cheapies I got in job lots with the cross feed knackered..........in fact ,if I got a 9" SB or Hercus tomorrow with cross screw failure,this is exactly what I would do.
 
If you used the 1/2", Roton has the LH and RH screws in ACME. They also have sleeve nuts to match which you might be able to fit in your existing nut and solder in place.

Acme Lead Screws & Nuts - Engineering Data | Roton Products Inc.

+1 Just use the Roton 1/2" components in their 8 TPI option and no need to mess with the dial graduations. It will also have the same "feel" you have become accustomed to, whereas the the finer pitch may take getting used to.

Not that it cannot be done. Your lathe, your rules.

Either way, nobody from Holbrook's design or QC department is likely to come knocking you up to complain.

:)
 
One of the most watched threads on metalworking is called EVANUT it deals with making a crosslide nut with Delrin. It’s easy to do.
 
If you're so inclined to make it yourself, Keith Rucker on YouTube made replacement acme cross slide and bronze/brass nut for his Monarch Model K, and also for a few other lathes for a couple of his viewers.

I personally wouldn't want to reduce the feed rate of my lathe by 25%, but rather keep it at 8 tpi. I've heard great things about those Holbrook lathes, but have never seen one in action, in person. Good luck with your project.
 
Thanks.. The lowest feed rate I have atm is 112 cuts per inch. Fine with HSS but bit hard on inserts.
 
I Would like to help anybody who is needing to make a Delrin or Acetal nut. The Evanut method is not good. No need to make it out of two halves. I have replaced both x and y on my Bridgeport and learned a lot. Cut the internal threads ACME style as you would with bronze. Cut at least 20 thou under. Heat up the screw with a blow torch while its turning in the lathe until it smokes, too hot to touch.
The Delrin nut will turn onto the screw with a big monkey wrench. Leave it to cool down. Minimum 1 hour. Heat the plastic with a torch or heat gun, don't heat the screw. It will turn off. One or two notches on the start of the thread on the screw with a hacksaw will help clean the nut up inside. It will be as close to a Zero backlash setup as you ever will get. If the screw was new, it would be Zero backlash.
 
I made a delrin nut, 7/8-4LH, using a tap I made from the same stressproof as the new screw. Fairly easy adternoon project once you have a good sketch to work from.
 
I don't see the difficulty making replacements. Get the dimensions off the leadscrew and nut. Reassemble your lathe. Make the leadscrew and nut. Install them on your lathe. Be sure to use bronze, not brass for the new nut. I suggest Stressproof or Fatigueproof for the screw. They machine nicely and have much better mechanical properties than 1018.
 
I have heard that my Harrison M300, made around 1976, has interesting leadscrew and cross slide screw. It is designed to be metric but they also made English ones. For those they used the same diameter screws just switched english thread pitches.
For example, from bad memory, the cross slide screw is 12mm diameter on both models but 10 threads per inch or the metric one is close to that pitch at 2.54mm.
Maybe you lathe is something similar where they upped the diameter to what seemed strong enough then used a nice even thread count.
Starrett uses a lot of oddball threads on their equipment. Some of it is legacy before standards existed and they see no reason to change and have to carry two sets of replacement parts.
Bill D

PS: yours sounds like 9/16 to me. 0.5625 while you have 0.556
 
Would it be worth recutting the original square thread screw on the flanks so that it is even along it's length and then adding an adjuster on the end of the nut to take up backlash? Or saw a slot near the end of the nut and add an adjusting screw to close up the last couple of threads and take up play?
 
I've made 9/16", 1/2" and 7/16" 10 thread acme screws and nuts before so that's an option. 8 pitch might be just a little harder since the tool will have a little larger nose than a 10 pitch tool, but should be straight forward. I make my internal tools by silver soldering a HSS tool bit on a grade 8 bolt and ground to fit the minor diameter of the nut. If the nut is fairly short this should work fine. I did have trouble one time threading a long 1/2" nut from a piece of aluminum bronze from hell so, as in all things, it depends, but worth a shot! I ended up making that one from a piece of brass and it came out fine. It all depends on how much it's going to be used and what kind of life you expect out of it.

Good luck,
Ted
 
I have heard that my Harrison M300, made around 1976, has interesting leadscrew and cross slide screw. It is designed to be metric but they also made English ones. For those they used the same diameter screws just switched english thread pitches.
For example, from bad memory, the cross slide screw is 12mm diameter on both models but 10 threads per inch or the metric one is close to that pitch at 2.54mm.
Maybe you lathe is something similar where they upped the diameter to what seemed strong enough then used a nice even thread count.
Starrett uses a lot of oddball threads on their equipment. Some of it is legacy before standards existed and they see no reason to change and have to carry two sets of replacement parts.
Bill D

PS: yours sounds like 9/16 to me. 0.5625 while you have 0.556


2.54 MM pitch is EXACTLY the same as 10tpi. good point on the 9/16, could be, .0065 difference seems like quite a bit though, did the OP check at an unworn end?

reminds me of the time quite a few years ago that I had a jacobs type chuck marked with a mounting thread of
"12.5 -1.25MM" looked for a while for an arbor for it, everyone gave me a funny look, then I finally tried it on a 1/2 - 20 and..it fit. well I felt a bit like the noobie sent to find a "lefthand pipe wrench" :rolleyes5:
 
....
"12.5 -1.25MM" looked for a while for an arbor for it, everyone gave me a funny look, then I finally tried it on a 1/2 - 20 and..it fit. well I felt a bit like the noobie sent to find a "lefthand pipe wrench" :rolleyes5:

Don't feel too bad. When I was starting out, I was sent for a left-handed screwdriver....

I actually spent 2 hrs looking until the shop foreman heard about it. Turned out to be a philips head, by the way.
 
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You did say little wear. I'd leave it be unless the nut is about to strip. I've a couple machines with a little wear and they work just fine. And there's Nothing cheap about a Holbrook!
 








 
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