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WoodSnarfer
11-12-2004, 09:12 AM
I've been looking on eBay lately, just trying to get the feel for what shows up out there for ball screws. For the machine I'm thinking about, I'd like an X travel of about 40". Those are the ball screws I've been searching out.

A couple I have looked at have the simple specs listed (e.g. .75" dia 44" long), and even have the mfr and part number (which is usually some sort of 16 digit alphanumeric string).

Next, I google the mfr and try to find the part number -- and here's where I get stuck. It's impossible (sometimes) to find anything out about the part.

So, how do you deal with this? If the thread pitch "looks" okay, and the part "looks" like it is high quality, and the price is good (like, $100 for a 40" screw with nut) -- do you just "go for it" and hope for the best?

Related question: As far as the ends of the screw go - do you figure you can have a machine shop tailor them to your needs at a reasonable cost, so again you don't really care how the ends are finished?

Thanks,
Chris

Al_The_Man
11-12-2004, 11:26 AM
I have picked up a couple of good ballscrew deals on ebay, a couple of things I look for is it a rolled screw or precision machined? A rolled screw can usually be identified by the small ridge or groove on top of thread and if it is rolled and a single nut, then generally it will not be pre-loaded and a small amount of backlash will be present, and it will not have the accuracy of a machined type, most rolled screws that are zero backlash have a double nut, the best choice is a machined screw, the most of which come with a pre-loaded nut. If you have the luxury of time, I would suggest hanging on for the machined type, they are very expensive new, but typically are 10c on the dollar on ebay NOS if possible.
In many cases you can adapt the machine to the ends, but you should be able to get a machine shop to turn or precision grind them down.
Al

buscht
11-12-2004, 11:33 AM
In my opinion, I only just go for it, if the price is around $25.
Usually, if you have a manufacturer's number, they have an 800 number and you can call them to ask specific questions. The numbers sometimes make sense and sometimes they don't. THe manufacturer will usually give you details fairly quickly.

You can always email the seller for more information. I have had good experiences and bad buying ball screws on Ebay. Be wary of ones that say "like new" , but don't give specifics ie: .001" backlash, no play, etc. I find that if the specifics are given, you are dealing with someone who at least knows what they are selling and its usually accurate. "Like new" could mean perfect to absolute junk.

Again, in my opinion, $100 for a 40" screw with nut isn't too much of a bargain, unless it comes machined ends and pillow blocks and is precision ground.

Be careful of shipping charges, some people charge $30+ for shipping.

You can buy brand new, rolled thread ball screws from Mcmaster Carr for $1.10 per inch and about $22.00 for a nut. 5/8" dia with .203" lead. These are very nice. I notice them on Ebay for considerably more. Be careful.

You can probably figure on about $35 to$50 per screw to get a machine shop to machine the ends, so if they are done already its a bonus. The problem then is that they are never machined exactly like you would want. You have to adjust your bearings and motor mount to suit. I guess its a tradeoff that you should decide upon, convenience versus cost.

ViperTX
11-12-2004, 12:11 PM
Well I bought a couple of ball screws on ebay, they were unused yet they were not exactly straight...luckily I got a refund less a restocking fee...*chuckle*...so, I'll stick with buying from McMaster Carr or from Thompson (sp?). You'll probably want to pick up 2 ball screw nuts for each ballscrew, so you can preload the ballscrews.

WoodSnarfer
11-12-2004, 12:25 PM
Well I bought a couple of ball screws on ebay, they were unused yet they were not exactly straight...luckily I got a refund less a restocking fee...*chuckle*...so, I'll stick with buying from McMaster Carr or from Thompson (sp?). You'll probably want to pick up 2 ball screw nuts for each ballscrew, so you can preload the ballscrews.

(thanks to the first two responders, also!) ViperTX - this raises another question...I was under the impression that I had to buy preloaded (or preload adjustable) nuts...when you say for me to pick up 2 ball screw nuts, how do you achieve preloading that way?

Do you bolt the nuts to the same hunk of aluminum, but "push" them apart to get them to shear against the screw in an opposing manner? Or something else? Also, is this more cost effective than just buying a preloaded/adjustable nut?

Thanks a bunch...I'm still designing my router in my head, but I have convinced myself that I'm going to build one of these, hopefully starting early next year.

Thanks!
-Chris

WoodSnarfer
11-12-2004, 12:35 PM
...You can buy brand new, rolled thread ball screws from Mcmaster Carr for $1.10 per inch and about $22.00 for a nut. 5/8" dia with .203" lead. These are very nice. I notice them on Ebay for considerably more. Be careful...

Thanks...I was looking at McMaster...question about that $22 nut -- it doesn't have a flange (the flange version is $51). If I wanted to use that nut, would I just machine an aluminum clamp/block to hold it to my axis?

Thanks,
Chris

buscht
11-12-2004, 12:38 PM
I use a rolled ball screw without a preloaded nut and am very satisfied.

Here are two differing opinions on how to make a preloaded nut from two knowledgeable sources.

http://www.homecnc.info/ballnuts.htm

http://www.industrialhobbies.com/ Click on the homemade ballnut label.

ViperTX
11-12-2004, 01:58 PM
Also http://www.homecnc.com has plans for $7 and industrialhobies.com wants you to buy their $176 preloaded ballnut. I ran across another guy that make his own and had some nice pics, etc. I have the reference at home and will update the info on Sat.

Bubba
11-12-2004, 04:08 PM
I made my own "pre-load" nuts for my machine and it was fairly simple to do. If you want to look at some pictures, check out my web site:

http://bellsouthpwp.net/A/r/Arts_home_page/cnc/

It shows the various parts as well as an assembled nut on one of the screws. If after review, you would like some "working" (read sketches etc) drawings in acad, let me know and I will forward them to you.

Bubba

ViperTX
11-15-2004, 10:18 AM
Okay here is the link I promised for Sat. http://www.tomsinstitute.com

Check out the Grizzly 1005 CNC retrofit. He has some nice zero backlash nuts that he made.

ViperTX
11-15-2004, 10:19 AM
Bubba,

Hey looks like you've done some great work. I'd love to see the acad files for your approach to zero backlash ballnuts. Thanks, Paul