Usual cost to turn down end of a ballscrew?

[WoodSnarfer]

I'm working out the design of my hobby/woodworking router...and I've come to the point where I really need to understand how I'm going to mount my ballscrews to the frame of the machine & to the gantry.

I read this thread:

http://www.cnczone.com/forums/showthread.php?t=2421

And I really like Jeff's drawing of the bearing mount. But, I am not a machinist, and I don't own any tooling to either turn or thread the ballscrew. Nor do I have the capability to drill out an aluminum (or brass?) block, to act as the bearing plate.

So, McMaster has ballscrew end mounts -- but the darn things are $311 each for 5/8" Seems excessive...so I was wondering:

If I were to bring my 5/8" (or 3/4") ballscrews to a machine shop, how much do you think I'd pay to have the end step-turned down (like in Jeff's drawing), and then threaded for the retaining nut?

Also, what do you think they'd charge me for drilling out a couple of square blocks of aluminum, for the bearing plates?

I'm going to get in my truck and visit a couple of local shops to ask them directly, but I wanted to be armed with some guidance from anyone here who knows that business, first.

Say, anyone reading this who can do this and is near Dutchess County, NY...are you looking for a new friend?

Thanks,
Chris

[ViperTX]

WoodSnarfer,
Your adventures should be interesting reading!

My last experience convinced me to buy my own mill-drill.

I suspect that turning, threading will most likely be about $200 to start.

Making the bearing plates....I suspect $400 for the first $150 for each additonal and you gotta provide drawings, tolerances, surface finishes...etc.

Anyway....Good Luck! Let us know what you find.

[buscht]

I had 4 turned down and threaded (both ends). My local machine shop charged 6 hours @ $35 per hour. $210 total for 4 pieces.

They said that it was a b*tch because the outer edge was very hard. I'm having 4 more turned down right now. I hope they have a better method and its cheaper.
T

[WoodSnarfer]

hmm...that's a good point...I wonder if there is anything that I could do myself to 'rough out' the portion I want turned, by grinding down the outer hardened surface.

My only metalworking tool is a big bench grinder...I wonder if it would be feasible for me to work the end of the ballscrew on the grinder, first, so the machine shop wouldn't have to burn so much time on their lathe (?)

I seem to remember the last time I tried grinding hardened steel on that grinder, and all the piece did was chatter against the wheel, so maybe that's a dumb idea...or maybe I need a different type of wheel.

$35/hour sounds like a pretty good rate for this kind of work.

-Chris

[buscht]

Somewhere on this forum are threads that show in detail how you go about grinding down the end of a ball screw. I think it was held in a lathe and ground down with a 4" angle grinder, but I'm not 100% sure.

Try doing a search

[coherent]

I went through the same delima as you and was surprised at the cost of having 6 5/8 ballscrew ends machined and 3 threaded, 3 with a flat for a couple setscrew. I decided to put the money toward a small metal lathe instead of toward the machinest paycheck.
I used a 4" grinder to grind away to the bottom of the ballscrew threads, then turned them down to NEMA 23 1/4" shaft size. Threading was fairly straightforward using a handheld die. A simple mount for me was to use a delrin "plate" with recesses (forstner bit same diameter as the bearing) and pressed the bearing into each side of the plate so the bearings were flush... mounted the plate(s) to each machine axis end (opposite the motor of course) using 4 simple "standoffs" which are just all thread couplers and button head screws of the same thread. Then a locknut and drop of locktite each side of the bearing hold the ballscrew in place. This will give you a inch or two (either inside or outside your axis end) and allow adjustment. You can use one at each end if need be. Cheap and very ridged.
If you'd like and it will help... send me a pm and I can take a closeup photo of mine and post it. Sorry I'm so far away or I'd be more than happy to help with machining your ballscrew ends. I figure the machining must be acurate enough, because I used a dial indicator to chuck them in a four jaw chuck and a micrometer to turn to within a couple thou.. I'm not a machinest by any means but it's a fairly simple process if you just take your time.
-marc

[KiwiOS]

Any decent job shop will have ceramic or diamond tooling that will take that hard surface off in less time than it takes to type this so it's probably not worth the risk of trying to rough the shafts freehand and scrapping them. Your problem with chatter when you try to grind hardened steel on your bench grinder is probably just an "out of balance" wheel or (less likely) what you had was carbide and not toolsteel or hardened steel. Anyway, a cheap Huntington Wheel dresser should help the chatter problem.

[WoodSnarfer]

Marc,
Thanks for the info & offer...yeah, NY to AZ is a bit of a trip!

I'll start hitting the yellow pages and probably take a couple of trips to local machine shops. Services seem to be pretty expensive in my neck of the woods, so I might also put this out as an RFQ and just ship the screws to someone who can do the work, when the time comes.

I have time...haven't even bought the screws yet. I'm trying to get a handle on my overall project costs.

-Chris

[buscht]

Another cost to keep in mind if you are using the cheap 5/8" ball screws from McMaster Carr. You need to find or make a mounting plate for the ball nut. It comes with a strange 15/16"-16 thread. I ended up buying mounting plates from Nook Industries for $20 apiece. In the meantime, I have bought a tap and will try to make my own mount out of a piece of aluminum angle.

[JFettig]

Its typically $50 an hour to have them machined at a shop.

I machined my ballscrew for my mini lathe on my mini lathe without annealing, it took a total of about 3-4 hours, I did it to see how possible it is, it took a c-4 carbide toolbit for each end(or resharpening), If they were annealed it wouldnt have taken so long. I tried using my cheap indexible tooling and they wouldn't work at all for some reason.

Jon

[WoodSnarfer]

Originally Posted by buscht Another cost to keep in mind if you are using the cheap 5/8" ball screws from McMaster Carr. You need to find or make a mounting plate for the ball nut. It comes with a strange 15/16"-16 thread. I ended up buying mounting plates from Nook Industries for $20 apiece. In the meantime, I have bought a tap and will try to make my own mount out of a piece of aluminum angle.

I think they have a flanged version of their cheap square ball nuts...for $33 more than the plain version.

I'm still bewildered by by the end blocks at $311 each.

-Chris

[Swede]

Guys, if you have a lathe (or a friend with one), don't shell out these outrageous sums! McMaster-Carr and other 5/8" & 3/4" ballscrews, while tough, are not extremely hard and can be turned and threaded without too much trouble.

Sorry if this post rambles, I am sick with the flu, drugged, and basically enjoying my buds on the Zone with no danger of transmitting viruses, unless its a "Kledge32 worm" or something equally evil!

The critical part is being sure that the turning and threading is concentric, meaning that the ballscrew blank must truly be centered, remain centered, and hopefully not dismounted until the job is complete. An eccentric bearing surface will probably wreck the job. Spend most of the time at the driven end of the balscrew. The simple end can handle slightly greater eccentricities than the driven end. Ideally both will be withn 0.0003" / 0.008mm or better.

You don't need a grinder! You can use abrasive paper with the proper technique. I've posted this link quite a few times. I guess turning ballscrews is a pretty common affair with guys like us.

The use of the plastic centering tube makes initial setup a snap. You'll need the following:

- Lathe with adequate through-hole, say a 10" swing or larger.
- a GOOD digital mike resolution 0.0001" or better
- A 4-jaw or adjust-tru 3 or 6 jaw
- tailstock center
- Delrin (acetal) plastic round stock, slightly larger diameter than the ballscrew
- Proposed bearings on hand for test fits
- A sharp carbide or HSS bit for roughing
- A specially ground finishing tool
- an assortment of silicon carbide wet/dry paper, 320 to 600 or finer, preferbly 1500 for finishing; auto parts store, lacquer finishing paper
- A good 0.0001" or 0.0005" dial indicator. The former is best.

The link describes the process. You can easily obtain +/- 0.0002" or better. There are a number of machine shops where the operator simply doesn't want to take the time to do it right, not understanding the stringent accuracy requirements. On the other hand, a larger shop with a true cylindrical grinder, and skilled operators, can do a better job than the one described here.

I'll caveat the need for 0.0003" runout - if you are setting up a 60" square wood router, you can accept higher runouts. If you are creating a highly precise bench mill with ground ballscrews and C3 or better accuracy, you'll want the lower runout.

Here's the links -

Shop made bearing block:
http://www.5bears.com/cnc04.htm

Turning a ballscrew for bearings:
http://www.5bears.com/cnc16.htm

You can practice this on a section of rolled ballscrew before chucking up your actual work.

Special super-high rake finishing tool for carbon steel: