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dockterj
03-03-2009, 12:24 PM
What is the most economical source for this? I need to replace the cross slide screw and nut on my Smithy. I don't want to use factory parts as I want to allow for more travel when milling. I've found this at MSC:
http://www1.mscdirect.com/CGI/NNSRIT?PMAKA=03777786
http://www1.mscdirect.com/CGI/NNSRIT?PMAKA=03778503
but I would need to buy 36" (i only need less than 18"). This is the the .003"/foot accuracy - they also have .009"/foot. Anyone else need 18" of 1/2-10 left hand acme threaded rod?

I'm thinking about using delrin for the nut instead of bronze.

Just Bob Again
03-03-2009, 12:51 PM
www.roton.com has all flavors of rolled screws. Accuracy is about .005/foot. 1/2-10LH is around $10/foot in steel and 15 in SS. They have nuts in bronze and plastic. www.mcmaster.com also has them. Maybe a bit cheaper. Both are a lot cheaper than MSC's $60.

atty
03-03-2009, 12:58 PM
I just went through this on my Logan cross slide, and I did the same thing you're doing....trying to get the pieces. I came to the conclusion that, unless I was doing a half dozen of these things, I couldn't beat the prices of the guys on Ebay selling the repair parts. IIRC at least one of them is offering custom work. Might be worth a look.

lazlo
03-03-2009, 01:06 PM
www.roton.com has all flavors of rolled screws.
www.mcmaster.com also has them. Maybe a bit cheaper. Both are a lot cheaper than MSC's $60.

MSC has both rolled and high-precision thread milled acme stock. Get it on the weekly 25% off sale, and its much cheaper than McMaster and Roton.

dockterj
03-03-2009, 01:13 PM
Wow! Roton is exactly what I was looking for. I'll probably do the leadscrew as well. What is an appropriate pitch for a leadscrew - 16tpi?

dockterj
03-03-2009, 01:19 PM
thanks Lazlo. Is the normal (.009"/foot) adequate for the cross slide as well as the leadscrew?

Just Bob Again
03-03-2009, 02:56 PM
MSC has both rolled and high-precision thread milled acme stock. Get it on the weekly 25% off sale, and its much cheaper than McMaster and Roton.

MSC's "precision" stock is also rolled and it's generally 3 tenths/inch. Maybe they have milled in some size, but not half inch. Also beware the difference between accuracy and backlash. The better-quality rolled screws like Nook are 3 tenths per inch (.004/foot) lead accuracy. Cheaper stuff can be a lot worse but most Keystone I've bought is within .oo5/foot. Backlash is generally around .009. To get less you need a split nut or similar.

MSC only sells in 3-foot chunks. Roton and McMAster sell in 1-foot increments. If you want cheap, Enco has cheap rolled stock. About $5 for a 3-foot chunk of plain steel in half inch. No left-hand, though. All right hand.

Carriage screw is normally a coarser pitch than crossfeed. 8 is typical on small lathes. I'd think 16 is too fine except maybe for a little tabletop machine. It's a long screw and needs to be stiff. half is too small. 3/4 is fairly common. If you have threading on that lathe, you want to keep the same pitch as original or you'll need new thread tables and maybe some odd change gears.

lazlo
03-03-2009, 03:31 PM
MSC's "precision" stock is also rolled and it's generally 3 tenths/inch.

No. Rolled acme stock is not precision -- it's 9 tho per foot accuracy, and has a 2G thread form that's intended for power transmission (jack screws and such):

http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=1907&PARTPG=GSDRVSM&PMT4NO=59444370&PMITEM=06054159&PMCTLG=00&PMT4TP=*LTIP

Nook precision acme stock is thread milled or ground, and has a 2C centralizing thread form intended for precision positioning. The milled acme stock is 3 times the accuracy of rolled stock: 3 thou/ft:

http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=3746&PMITEM=00277194&PMCTLG=00

The Nook ground acme stock is 3 tenths/ft, but MSC doesn't carry it, and it's very expensive.

DocterJ:, here is a 3 foot section of the Nook precision 1/2 - 10 Left hand acme rod. MSC's regular price is $61, so it will be around $45 with the 25% off sale later this week...

http://www1.mscdirect.com/CGI/NNSRIT?PARTPG=IMLMKD&PMPXNO=1723155

Just Bob Again
03-03-2009, 06:19 PM
No. Rolled acme stock is not precision -- it's 9 tho per foot accuracy, and has a 2G thread form that's intended for power transmission (jack screws and such)

Nook screws are rolled with a 2C thread and accuracy of 3 tenths/in or .0036/foot. Their milled screws aren't quite twice as good at 3 times the price.

From the Nook Industries website -

Nook PowerAc™ Acme Screws are manufactured with centralizing thread form to prevent wedging. Nuts including bronze, plastic and anti-backlash styles are matched with over 110 screw diameters and leads. Acme screw lead accuracies:

Rolled +/- 0.0003"/"
Milled +/- 0.002"/ft.
Ground +/- 0.0005"/f

Evan
03-03-2009, 06:22 PM
You can buy direct from Keystone Threaded Products. Theirs is rolled stock and very inexpensive. It is 2C centralizing lead screw stock.

I used it on my mill and it works fine although it does have an error as stated of around .009 per foot. I think I paid about 3 or 4 bucks per 3 ft piece for 1/2 x 10 LH a few years ago. The .009 error is very consistent and can easily be compensated by altering the steps per unit value very slightly on a CNC machine.

Delrin has worked out very well on my machine and it sees a lot more wear than a manual machine will because of the much higher rpm of the leadscrew. I have both bronze and Delrin leadscrew nuts on my mill and while I have to adjust the bronze nuts from time to time I have not yet adjusted the Delrin nut on the Y axis. It is now up to a whopping .0005" or so backlash so I guess I will have to do something about it in the next few years.

wtrueman
03-04-2009, 12:02 AM
Possibly look at a woodwork forum as I used to need some to make my own parallel jaw wood clamps. Otherwise hold on to it as you'll probably need it for some other project six weeks down the road LOL. Wayne

What is the most economical source for this? I need to replace the cross slide screw and nut on my Smithy. I don't want to use factory parts as I want to allow for more travel when milling. I've found this at MSC:
http://www1.mscdirect.com/CGI/NNSRIT?PMAKA=03777786
http://www1.mscdirect.com/CGI/NNSRIT?PMAKA=03778503
but I would need to buy 36" (i only need less than 18"). This is the the .003"/foot accuracy - they also have .009"/foot. Anyone else need 18" of 1/2-10 left hand acme threaded rod?

I'm thinking about using delrin for the nut instead of bronze.

wierdscience
03-04-2009, 09:23 AM
Acme threaded rods and more-

http://www.greenbaymfgco.com/catalog.php