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Stu
03-11-2015, 03:21 PM
I want to drive the leadscrew of my lathe from the opposite end with a dc gearmotor. The problem I am having is figuring out how to attach an extension to the end of the leadscrew for a pulley or gear. In the picture you can see the end I’m talking about. There are thrust bearings on each side of the end block and the nut is a locking type that holds the adjustment. I would prefer to have something that is reversible, but realize that may not be possible. One thought is to bore the end and press fit an extension on. Another would be to grab the nut with a socket and build an extension from that, but I can see the motor loosening or tightening the lock nut and losing the tension on the thrust washers. If I were to make a longer nut with set screws with lead or brass pads to protect the threads, would the set screws have enough holding power to keep nut from coming out of adjustment? Any thoughts on what would work?
http://i913.photobucket.com/albums/ac334/bstupak/leadscrew_zpslzcz58dv.jpg (http://s913.photobucket.com/user/bstupak/media/leadscrew_zpslzcz58dv.jpg.html)

Stu

Doozer
03-11-2015, 03:41 PM
File a flat on the threads to accept a set screw lock
and make the bore of your coupler threaded.


-D

Carm
03-11-2015, 04:04 PM
Well, I have a couple ideas, but I need to know about the thrust bearings. Are they ball/needle or bearing material like bronze? What is the keeper thread - 1/2/13, 3/4-10 etc. (60deg.?)

Black_Moons
03-11-2015, 04:33 PM
Attach a pulley to the leadscrew, on the shaft side of the block? Might lose an inch or two of travel on your carriage but..

Hopefuldave
03-11-2015, 04:37 PM
Drill the end of the leadscrew and silver solder in an extension slightly smaller than the thread's minor diameter? Choose your extension from hex, keywayed shafting etc.

Stu
03-11-2015, 04:57 PM
Well, I have a couple ideas, but I need to know about the thrust bearings. Are they ball/needle or bearing material like bronze? What is the keeper thread - 1/2/13, 3/4-10 etc. (60deg.?)

The thrust bearings are roller type and the thread is 1/2-20

Stu

Stu
03-11-2015, 05:01 PM
Attach a pulley to the leadscrew, on the shaft side of the block? Might lose an inch or two of travel on your carriage but..

That's very interesting, there is a 3/4" space from the leadscrew to the lathe bed and the LS has a keyslot. I really won't miss a couple of inches of carriage travel. I like that, I'll have to checkout the needed pulley sizes.



Stu

Stu
03-11-2015, 05:10 PM
Drill the end of the leadscrew and silver solder in an extension slightly smaller than the thread's minor diameter? Choose your extension from hex, keywayed shafting etc.

I like that way too, but would I weaken the shaft by leaving such a small amount of material under the threads. The shaft end is 1/2"-20, minor dia is .435, wouldn't a smaller bore maybe .250 be better?

Stu

Carm
03-11-2015, 05:58 PM
Turn a round hunk o'stuff that has clearance from the mounting bracket (the two allen heads). place a jam nut in lieu of the full hex nut in place. Either blind bore and thread/tap 1/2-20 or get out to the end of the threads and fasten a cap that has your desired pulley that features a pilot hole that acts as a drill bushing into the outer periphery of the lead screw end (or 1/2-20 0 minor diameter). Draw the ass'm up snug, drill the hole with a hand drill, ream for a dowel or roll pin. You won't have to take anything apart ('cept that full nut) and won't have burrs that could make you cuss when you want to remove...just back off the jam nut.
You could c'bore the leadscrew end over the jam nut and setscrew on a flat if you think that is necessary.

Hopefuldave
03-11-2015, 07:33 PM
I like that way too, but would I weaken the shaft by leaving such a small amount of material under the threads. The shaft end is 1/2"-20, minor dia is .435, wouldn't a smaller bore maybe .250 be better?

Stu

That's pretty much what I meant, the actual extension would want to be smaller than the thread's minor diameter so you could get the nut and bracket off, the spigot going into the leadscrew could be a fair bit smaller - there's probably a formula in Machinery's or similar for equal torsional shear strength in the hollow leadscrew and the spigot if you're pernickety!
The deeper you drilled the screw (and the longer the spigot), the more strength the join would have, I'd guess the limiting factor would be the spigot's torsional load, chamfering the leadscrew bore and matching it with a "cone" where the extension fits into it might help reduce stress raisers and make it a little stronger (especially if the two conical faces got some silver solder too) - I guessed that last bit!

J Tiers
03-11-2015, 08:19 PM
This is not, or SHOULD NOT BE, a high strength issue.... if you reef on the leadscrew that hard, you will likely pretzel the lathe as well...

So, back to reality....

One way which should carry all that you need to carry load-wise, is to drill the end for a stub shaft, turn it and put it in, then cross-drill for a pin to hold them together. If the pin ends up under that nut, it will be held in and be secure.

garyhlucas
03-11-2015, 08:26 PM
Try McMaster Carr Part # 3084K31. Tap the unmachined end to match the thread. Looks like the torque rating would be just fine.

Lee Cordochorea
03-11-2015, 09:47 PM
Drill 2 or three holes in both lead screw end and separate pulley shaft. Attach with roll pins. (Will, of course, need some kind of bearing for pulley shaft.)

1-800miner
03-11-2015, 11:50 PM
You might want to consider getting rid of the home made heavy duty lead screw support and going back to the original Zymac support.
They made them flimsy on purpose, it fails rather then sending the lead screw through the gear train.

Grind that nut down to half the thickness and you will have a little more shaft to work with.

darryl
03-12-2015, 12:55 AM
A few thoughts- in use the lead screw is driving the carriage towards the head stock for the most part, so the thrust bearing would be on the left side of the bushing support. You would probably want a permanent shoulder on the lead screw on that side so that nothing shifts unexpectedly in use. That leaves the threaded portion to the right of the bushing for the nut to go on, and that's where the play would be taken out. At the same time it makes it impractical to drive the lead screw from the nut itself. Otherwise you could just put a roll pin through the nut and screw, then turn the nut to turn the screw.

Perhaps this still would be the best way to do it- drive the nut, which you pin to the lead screw shaft. Make the play adjustment before cross drilling for the roll pin.

Perhaps the more difficult thing to do is to align the drive with the lead screw so a positive engagement can be made without play, and without binding.

Barrington
03-12-2015, 06:30 AM
Simply mill the end of the leadscrew to form one part of an 'Oldham' style coupling. (Either a groove or a tongue, whichever's easier.)

As a bonus the alignment of the drive to the leadscrew becomes non critical, and the drive can be taken off or replaced with minimal fuss.

Cheers

.

Stu
03-12-2015, 08:01 AM
You might want to consider getting rid of the home made heavy duty lead screw support and going back to the original Zymac support.
They made them flimsy on purpose, it fails rather then sending the lead screw through the gear train.

Grind that nut down to half the thickness and you will have a little more shaft to work with.

For this model -101.28910- it is the original support, at least that's what it shows in the manual parts list. There is a clutch on the end of the QC gearbox to prevent that

Stu

Stu
03-12-2015, 08:09 AM
A few thoughts- in use the lead screw is driving the carriage towards the head stock for the most part, so the thrust bearing would be on the left side of the bushing support. You would probably want a permanent shoulder on the lead screw on that side so that nothing shifts unexpectedly in use. That leaves the threaded portion to the right of the bushing for the nut to go on, and that's where the play would be taken out. At the same time it makes it impractical to drive the lead screw from the nut itself. Otherwise you could just put a roll pin through the nut and screw, then turn the nut to turn the screw.

Perhaps this still would be the best way to do it- drive the nut, which you pin to the lead screw shaft. Make the play adjustment before cross drilling for the roll pin.

Perhaps the more difficult thing to do is to align the drive with the lead screw so a positive engagement can be made without play, and without binding.

There is a shoulder on the end of the LS, Thrust bearings are on both sides of the hanger. The LS is slid into a clutch on the end of the QC gearbox and is driven by a key.

yf
03-12-2015, 01:50 PM
just cross drill the nut and pin it.
then drive the nut with a cheap hex socket with a set screw to hold securly on the nut.
Quickly done and reversable.

ulav8r
03-12-2015, 11:54 PM
Replace the current nut with a thin jam nut, then add a coupling nut that you can attach a threaded extension to. Adjust the jam nut for proper tension against the thrust bearings, then hold it there as you tighten the coupling nut to lock it there.

darryl
03-13-2015, 12:42 AM
Perhaps you are only using this 'external' drive method to give a power feed for turning. If so you don't need a solid drive that's free of play. I kind of went on the assumption that you would want a precision rotational control from the drive to the lead screw. You could pin the nut as I suggested, then drive the nut using a hex socket, but you would require a well aligned setup and also have to bond the socket to the nut to eliminate backlash in order to get that kind of precision. Doable but finicky. If that isn't required, then many methods would suffice- the oldham coupling sounds good.

Stu
03-13-2015, 08:21 AM
Thanks for all the ideas, guys. I am going to try adding a pulley or gear just ahead for the mount first and try to drive it from there. I like this as it is completely reversible. If that fails I'll try the reduced jam nut with a threaded coupling and pinning. I'll post any results.

Thanks, Stu

Arcane
03-13-2015, 08:50 AM
I'd replace the nut with an internally threaded shaft that would mate up nicely on the outboard end with whatever you wish to use to drive the whole kit & kaboodle. Rather than trying to use jam nuts or pinning it to the lead screw, I'd use high strength Locktite to secure it.

Doozer
03-13-2015, 08:51 AM
http://images2.mcmaster.com/Contents/gfx/large/6410k33p1-d03cl.png?ver=15579756
$36.00 Each

6410K41


For Shaft Diameter (A)
3/8"


For Shaft Diameter (B)
3/8"




I did the same thing to my 10" Atlas POS lathe.
Used a Ford Taurus windshield wiper motor from the '90s.
I used the McMaster Carr purchased rubber coupling (above)
and threaded the one end for 1/2-20 thread. (Have to make
a mandrel to hold it straight in the lathe when threading it,
as it is rubber between the steel inserts.)
Then used a set screw with a 1/8" dog point to go into the
keyway on the leadscrew shaft. Used a variac to control the
motor.

--Doozer

micrometer50
03-13-2015, 02:10 PM
Didn't Evan do something like this.Does anybody have a link to his site.

macona
03-13-2015, 09:44 PM
Looks like the nut is a lock nut so you should be able to drive it with a socket. Backlash won't matter, this is just for feed.

Though I would try to drive the hand wheel somehow instead of the leadscrew, otherwise you just wear out the screw for when you need to use it for threading.

caveBob
03-13-2015, 10:13 PM
FWIW, what I did... just turned a small internally threaded hub, screwed onto leadscrew/then cinched in place with a setscrew pushing down a brass plug. Bolted pulley on outboard side of hub:

http://oi47.tinypic.com/i27v2p.jpg

http://oi47.tinypic.com/5xmo8g.jpg

http://oi49.tinypic.com/kcywaq.jpg

http://oi47.tinypic.com/2irkso1.jpg

More here (http://www.machinistweb.com/forum/showthread.php?t=1413&page=4&highlight=powered+leadscrew) if you're interested...

Abaker
03-14-2015, 08:18 AM
Another idea - Get a split taper pulley bushing and machine it to fit the thread on the end of the leadscrew. Replace the nut with the bushing and instal pulley. Should be able to drive in reverse and shouldn't have to mod the lead screw or bracket.

oldtiffie
05-01-2015, 10:10 PM
Simply mill the end of the leadscrew to form one part of an 'Oldham' style coupling. (Either a groove or a tongue, whichever's easier.)

As a bonus the alignment of the drive to the leadscrew becomes non critical, and the drive can be taken off or replaced with minimal fuss.

Cheers

.

Fully agree - good choice - and a myriad of variations to/of the basic principle with no loss of drive rotation.

https://www.google.com.au/search?q=oldham+coupling+application&sa=X&rls=com.microsoft:en-AU:IE-SearchBox&rlz=1I7IRFC_enAU360&biw=1536&bih=706&tbm=isch&tbo=u&source=univ&ei=ujBEVbDLO5SdoQTszYHABA&ved=0CFAQsAQ

https://www.google.com.au/search?q=google&rls=com.microsoft:en-AU:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7IRFC_enAU360&gfe_rd=cr&ei=djBEVcWFBtDu8wfE34EY&gws_rd=ssl#rls=com.microsoft:en-AU:IE-SearchBox&q=oldham+coupling+application&revid=1844146628

A really priced and functional shaft-to-shaft positive connection with quite a bit of allowance for shaft-to-shaft centre/axis misalignment.

flylo
05-02-2015, 08:56 AM
Why not use a half thickness nut to give the clearence you need. Nice work CaveBob!

Stu
05-02-2015, 11:50 AM
I finished the project

http://bbs.homeshopmachinist.net/threads/66794-Extension-to-leadscrew-finished

Stu