Turning the End of Hardened Bore Screws

[Texasbowhunter]

Needing some direction on this...I'm going to build a 3-axis cnc machine and the linear rails and threaded bore screws are of concern...
Cutting the linear rails won't be a problem with a radiac metal cutting blade in my 4.5" angle grinder...Thats resolved
It's the hardened threaded bore screws that may be of concern attempting to cut down to length I desire and there for creating the same profile on the end as comes factory...
I have seen videos of a guy turning them down with tungsten carbide or another who heated up the end to soften the material so the cutter can do its job...Don't know if he re-hardened though
So, before I take on a project like this, I was hoping to get some thoughts and ideas to possibly make the frustration tolerable on my end...
Thanks in Advance
Paul

[Tobias-B]

Do you need to profile the ends?

Cutting and chamfering with the angle grinder and a thin abrasive blade works fine-
it's a bit slow, if you don't want to kill the temper, but otherwise leaves a good finish.

For profiling (cutting a slot, cutting down to make a spigot, etc) grinding in a lathe
(and yes, you can make up fixtures to do it in a drill press with an angle grinder, etc)
is ideal.

hth,
t

[JRouche]

Needing some direction on this...I'm going to build a 3-axis cnc machine and the linear rails and threaded bore screws are of concern...
Cutting the linear rails won't be a problem with a radiac metal cutting blade in my 4.5" angle grinder...Thats resolved
It's the hardened threaded bore screws that may be of concern attempting to cut down to length I desire and there for creating the same profile on the end as comes factory...
I have seen videos of a guy turning them down with tungsten carbide or another who heated up the end to soften the material so the cutter can do its job...Don't know if he re-hardened though
So, before I take on a project like this, I was hoping to get some thoughts and ideas to possibly make the frustration tolerable on my end...
Thanks in Advance
Paul

I have use inserts for cutting hardened rod in the lathe before. And really didnt even have to pay attention to the shape or grade.. If I need to cut carbide bar in the lathe I use CBN inserts. JR

[mtraven]

"hardened threaded bore screws" --what exactly is that? a hollow screw? or are you talking about shortening a screw, or opening up/ making a bore? Pic would be great.

how hard we talking? I've faced off ball bearings in the lathe with inexpensive carbide(brazzed) tooling. I've also turned down old CV shafts (from cars) & they are pretty damn hard. Solid carbide / indexable carbide mills will do the same thing on the mill. Then there are cbn & ceramic tools--as JR said, those can cut carbide.

Alternatively, I've used a very basic grinder setup (4" bench grinder), bolted to the lathe to size the length of engine valves. Only reason I did that differently was because I needed more precision (0.0005") than cutting would offer.

[BCRider]

I'm thinking solid carbide drills for holes. And from there carbide tooling for boring or turning. This is likely also the right time to use the plain flat topped inserts that also seem to have the sharpest edges to them. Although JR says he didn't have any issue with the usual molded shape types I'm sort of thinking that a keen edge would make it easier to get an accurate size by easily scraping the metal away rather than needing to first dig into it and set up a chip.

[Bented]

What is a bore screw ?

[sarge41]

I'm like the others, what is a bore screw?
Sarge41

[Texasbowhunter]

I was under the impression they were called a bore screw, but it seems they may be called a linear motion ball screw

[Texasbowhunter]

And yes, I would need to profile one end...the end that would get profiled would NOT be the end where the threaded portion is
The end I would profile would be just a reduction to a specific size by a given length...Kinda turn down the threaded portion to fit in a bearing cleanly then somehow cut a ring for a circular clip to retain the screw inside the bearing block
Thanks to all that has suggested something to help make life easier
Now as far as I know the screw is hard all the way thru just very hard
I have no means of a grinder attachment to profile the area of concern that may have to get resized and profiled...
Paul

[Texasbowhunter]

Here's a good picture on the end I may need to re profile in a ball screw
The lower left-hand side
Paul

[darryl]

Seems to make sense now. Cutting to length you have figured out. How to machine the threads off for 3/4 inch or so is handled by the right cutting tools, as suggested. Having that machined part concentric with the threads is what you need to resolve. I would handle that by mounting a piece of aluminum in the lathe and boring it for a close fit for the OD of the threads. The idea is to push the ball screw in from the left with only enough sticking out to work on. Then tighten the chuck jaws to crush the aluminum down onto the ball screw. This means you start with the aluminum piece being not much larger than the OD of the ball screw to begin with.

The left end of the ball screw gets wedged in the spindle bore to keep it from flopping around. It needs to be closely centered here as well. Play with shims to achieve this. If your spindle bore cannot accommodate the ball screw, then you can't do it this way.

[Bented]

I see, turning a ball screw end.
At the shop where I currently work we turn them often in the hardened state using hard turning tools, not as fast as annealing the ends first as we only do 10-30 parts per job.

If only a handful of parts look into hard turning tooling, speed will be your friend.

[Texasbowhunter]

[QUOTE=Bented;n2005547]I see, turning a ball screw end.
At the shop where I currently work we turn them often in the hardened state using hard turning tools, not as fast as annealing the ends first as we only do 10-30 parts per job.

If only a handful of parts look into hard turning tooling, speed will be your friend.
[/QU
What type of hardened tools does the shop use? carbide? or Harder if there is something harder?

[mtraven]

"I have no means of a grinder attachment to profile the..."

if you have a lathe & a grinder, you do have the means. Took me less then a day to fab some mounts. I dont use it often, but it is handy when I need it. Since you said "really hard" rather than listing a measurable hardness (ie rockwell), you might be better off investing your time & money in a grinder?

But I dont think you have to, as I said, I've done ball bearings with carbide...I doubt your leadscrew is harder than that (might be just as hard though). Your tools is gonna need a pretty big radius & as a result you'll need a little more horsepower, 3/4hp & over will do fine...stuff I did was with a 1/2hp loaded pretty hard.

The real challenge, as several others have indicated, it workholding. Specifically doing it concentrically, rigidly...you'll find hard materials dont want to say locked in a chuck. Then there is the challenge of keeping the tail end of whipping around. ddarryl's method is solid, I'd suggest you build a spider...not the chuck side shim type spider, but basically a 4 jaw chuck on the rear end of your spindle...its just more versatile. I made one a few years ago, another thing that I dont use often, but when I need it, its there.


lastly, i'll remind you that if you dissemble the ball screw nut (take the balls out). There will likely be two sizes of balls in there: the bigger load bearing balls & the marginally smaller spacer balls. Generally they alternate. Make sure you get them back together right, with no contamination.

[elf]

I would redesign the CNC machine to fit the ball screws