Would 3/4" 8 tpi 2C acme thread be compatible with my heavy 10 3/4" 8 tpi lead screw?

[Red1fire]

Would 3/4" 8 tpi 2C acme thread be compatible with my heavy 10 3/4" 8 tpi lead screw?

Would 3/4" 8 tpi 2C acme thread be compatible with my heavy 10 3/4" 8 tpi lead screw?



Here is the acme threaded rod i am looking at.

3/4-8 Thread, 6 Ft. Long, 1 Start, Right 6184 - MSC

 

[jonesturf]

Email Ted at [email protected]. He might have something. I looked into that kind of product and the accuracy wasn't there. You want a ground leadscrew. It would work but it's tolerances won't meet original specs. You can always email them and ask them how much error there isin their threads.

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[jonesturf]

Looking back through my emails with him he said the error was no more than 0.0005" per foot from South Bend. He has some from other machines you could use to make one. That's what I'm doing with mine.

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[johnoder]

Easy to see here at Lodge & Shipley that extreme care went in to making their lead screws. Two steadies (on carriage) and one follower rest in the set up

http://img.photobucket.com/albums/v337/johnoder/24 X 168 LS/Lead Screw Scan/LeadScrewSetUpSM.jpg

 

[thomasutley]

Easy to see here at Lodge & Shipley that extreme care went in to making their lead screws. Two steadies (on carriage) and one follower rest in the set up

http://img.photobucket.com/albums/v337/johnoder/24 X 168 LS/Lead Screw Scan/LeadScrewSetUpSM.jpg

That's a really interesting photo, John. Still begs the question of how to make the leadscrew that makes other leadscrews...? How did they make the first accurate screw without an accurate screw?

 

[johnoder]

That's a really interesting photo, John. Still begs the question of how to make the leadscrew that makes other leadscrews...? How did they make the first accurate screw without an accurate screw?

Measure inaccuracies and build compensating devices is what the old timers did. Rogers Bond? or was it another?

 

[TeflonDave]

Measure inaccuracies and build compensating devices is what the old timers did. Rogers Bond? or was it another?

Nice - that's why there is lead and pitch in the screw thread definitions

 

[Red1fire]

Thanks Tom, picked up a Lead Screw for 9 or 10K Lathes 50-3/8" OAL 42-3/8 Threads .75" Loc: G 3 Should have enough room to flip it not even have any worn out sections. Need help on what type of gear box end will fit my heavy 10R. Anyone with info please don't keep it to yourself.

 

[4GSR]

Just a little F.Y.I.

The PD tolerance for a 2G cut thread for this size is about .0158". This is basically the same tolerance for a 2C cut thread, too. For a 3G or 3C PD tolerance is .0074". Most threads are cut to a more consistent tolerance that this on a lead screw but can vary this much part to part. Ken

 

[swells]

As the lead screw machine warmed up and was dialed in, the screws were sorted into: very high tolerance(government build specs)next was Tool Room lathes, and so on. Measured over wires. Remember, SBL was making their lead and feed screws before the ASME/ANSI standards. I have the only running SBL Automatic Feed screw machine left in the world...lol It takes me a bit to dial it in after warming up, but it will still run screws at the high print tolerance over wires.
2C is far to sloppy for a lead screw, and I believe the screws were all High G class anyway.

Steve

 

[thomasutley]

As the lead screw machine warmed up and was dialed in, the screws were sorted into: very high tolerance(government build specs)next was Tool Room lathes, and so on. Measured over wires. Remember, SBL was making their lead and feed screws before the ASME/ANSI standards. I have the only running SBL Automatic Feed screw machine left in the world...lol It takes me a bit to dial it in after warming up, but it will still run screws at the high print tolerance over wires.
2C is far to sloppy for a lead screw, and I believe the screws were all High G class anyway.

Steve

Steve,

What are our options if we need new Acme stock? Are you in a position to offer new ones for sale? And by new ones, I mean either complete screws or straight thread stock we can graft onto gearbox end stubs.

I recently cut and flipped my 16" X 8' bed screw, but my first choice would have been to replace it as a wear item.

Thanks,

Tom

p.s. We'd love to see the SBL screw machine in action. Have you ever posted photos or video of it somewhere?

 

[SBLatheman]

Easy to see here at Lodge & Shipley that extreme care went in to making their lead screws. Two steadies (on carriage) and one follower rest in the set up

http://img.photobucket.com/albums/v337/johnoder/24 X 168 LS/Lead Screw Scan/LeadScrewSetUpSM.jpg

South Bend Lathe had several machines used to cut the threads on their leadscrews. I don't remember the brands (there was more than one). Acme rings a bell.
Each machine had several traveling steady rests, and a follower rest right by the tools.
They had no gearbox, but an alaberate step up of change gears. They could adjust the lead by tenths of a thousandth of lead per foot by changing some gears.
BTW: the first screw cut on each machine was a replacement screw for that machine
The machine that Steve Wells has was made by SBL to cut crossfeed screws and compound screws. It has a a similar design for the tooling set up and follower rest as the leadscrew machines had.
Ted

 

[swells]

Steve,

What are our options if we need new Acme stock? Are you in a position to offer new ones for sale? And by new ones, I mean either complete screws or straight thread stock we can graft onto gearbox end stubs.

I recently cut and flipped my 16" X 8' bed screw, but my first choice would have been to replace it as a wear item.

Thanks,

Tom

p.s. We'd love to see the SBL screw machine in action. Have you ever posted photos or video of it somewhere?

Tom,
I've spent about 2 years converting the machine over to 24V input controls with a Hitachi L100 inverter with programmable input functions to run a new Mac Air control and motor reversing/carriage movement stops and saddle movement from front to rear cutting all automatic. I've been sick for the past 6 months, but am much improved now, so i'm trying to catch up. I rebuilt a tool room 10L in that two years to use as a first operation lathe for the cross feed screw stock. I'm only making the 7/16-10 LH stock, and need a couple more months to catch up. I'm also making 10L-R cross feed nuts to trade with Ted for Workshop nuts...almost through with the setups for production. After Ted inspects them, I'll list a few for sale, along with the cross feed screw stock again.
I have a few videos of the screw machine running, haven't posted them yet, I will.
On the lead screw stock, I believe you have done the most economical repair possible, and would do that too or find a very good used screw, albeit the sources are limited.
a few pictures from Ted attached.

Steve

 

[stephen thomas]

The advertised tolerances for Nook rolled thread leadscrews is .0003"/inch +/-.

This may seem "huge" but how many of us use our SB's to cut other leadscrews?
How many of us have original leadscrews with that much wear in some sections?
If you buy any leadscrew stock and plane a slot in it, it will warp. If the concern is 10ths, how much does the length change when it is straightened?

When I replaned a 54" bed and put it under my formerly 4' 10K I just went with a Roton rolled thread leadscrew and made the spliced on end for the gearbox here. It will be necessary at some point to make a cross-slide screw for the same lathe. I'm pretty comfortable that given the aprox 4" of useful cross travel, when making that screw, a total error of up to .0014" in that distance will never be an issue in use. First, the error is probably not completely uni-directional and may be less cumulatively. Second, I don't think I've ever seen a 9" or 10K that did not have more than that error due to differential wear of the cross slide screw.

Beyond that, a 10K will not be my choice for making other leadscrews, or screws for diffraction gratings or ruling engines. For any other fits or typical bolts, .0003"/inch will be within my needs if it is even that bad.

I did send Roton an email requesting info on their tolerances for 3/4"-8 rolled thread leadscrew, and what the cumulative tolerance is over 3'. Maybe they will reply next week. At some later date when time permits, I'll get out the gage blocks & .0001" indicators and see what mine actually does as installed.

SB leadscrews were apparently made exceptionally well. None other than late PM'r Jim Kizales (whose career started with NBS) said SB precision leadscrews made them the go-to machines for some close ops there. Out in the field of us regular users, though, the worn leadscrews, not to mention the rest of the lathe, probably fall a good bit shorter. SB made really good & accuraate parts and assemblies, but they tended to use soft easy to machine materials that wear quickly. I'll worry about nanometer tolerances on a leadscrew if time ever permits rebuild on one of the Hardinge TL's here. Until then, my SB is back in sound operating condition quickly and inexpensively, soldiering on doing everyday tasks it is so practical for.

smt

 

[thomasutley]

Nice seeing the setup for planing the keyway. Out of curiosity, how much did the screw warp?

 

[stephen thomas]

Thomas-

The leadscrew installed on the 54" bed is about 47.5" long including the splice section and TS end journal. Looking at the planer pictures & considering my fading memory, I think I planed a 5' length to start. I bought much longer than needed because it did not make Roton's $80 minimum anyway. The extra length also helps when straightening.

The warping was minimal - ISTR around 1/8" in 5' length. Certainly not 1/4". I pressed it out on wooden blocks, by hand, on the planer table, and rolled it to check progress. I may have used a clamp & wooden pad near the ends a few times.

After shortening the planed, over-length screw down to rough length the set up to turn the ends included dialing in the 4J chucks (one on the nose is actually an Adjustru) at each end of the spindle here, and then putting a center pop in the end. This may have been a few .001's off center from the body of the screw, as "unbent". But letting the ends free for the center pop added to the straightening process as the journal and splice would then be concentric with the body.

smt

 

[swells]

Stephen,
I searched for stock several years ago for feed screws and never found the specs I was looking for without paying through the nose for it. most stocked sizes were below specs. I finally found Rolled Threads Unlimited in Wisconsin and they rolled 3G for me which made it into the higher side of the .003 backlash. The lead error was .00025 per inch or .003 per ft. but I had to purchase about 1500.00 to get the price per ft down to a reasonable cost. The screw blanks I have run on the SBL machine are much better. South Bend taps for feed nuts were not a standard size, They fall between 4G and less than 5G. high precision Lead screw stock would be, I presume, very costly. When you get ready to replace the cross feed threads, let me know and I'll send you a repair blank and you can try it.

Steve

Steve

 

[stephen thomas]

Swells-

That's a great offer!
Now to accrue some round-to-its.

On May 14 I sent Roton the following email:

"What is the pitch tolerance for your rolled thread leadscrews? 3/4 - 8 RH acme, specifically?

inch/inch or inch/ft? and cumulative over say 1 ft and 3 ft?
Is there a table on your site that I am missing with these values listed?

Thanks!
smt"

Today I sent it again with the notice "Second Request"

Not impressed with their responsiveness.

smt