How to machine a ball screw
I've just received some Chinese 1204 ballscrews that I ordered a couple of weeks back for the CNC conversion project on my Chester 16V mill. I bought them with no machining because I thought I could just machine the ends myself to fit the mill. I knew the screws would be hardened but I didn't appreciate just how hard ! My regular HSS lathe tools just bounce. Is it possible to machine these ballscrews with carbide inserts or should I find a machine shop to grind them for me (though that would probably cost more than the screws themselves).
Any suggestions would be appreciated
Re: How to machine a ball screw
Re: How to machine a ball screw
I did a 1604 ballscrew for a chap on here the other week
Just used a carbide tip it did bounce around a bit but once you get under the crust its ok
Re: How to machine a ball screw
it depends on your lathe's power. I have machined ends on my little chester using carbide tipped tool
You do need to take a deep cut starting at the face of the screw. It will glow red and so keep a fire extinguisher handy.
Re: How to machine a ball screw
I have not tried to machine ballskrew ends yet but on other hardened stuff I just put it in the lathe and grind the first bit off with a handheld angle grinder while its spinning so you don't get it out of round too far and then machine from there. Depending on how tough the steel on the inside is, you might get away with HSS tooling once you grinded away the chrome and thin case hardened layer.
Re: How to machine a ball screw
This could be the perfect opportunity to build a toolpost grinder for your lathe ;-)
- Nick
Re: How to machine a ball screw
Quote:
Originally Posted by
komatias
it depends on your lathe's power. I have machined ends on my little chester using carbide tipped tool
You do need to take a deep cut starting at the face of the screw. It will glow red and so keep a fire extinguisher handy.
My lathe is a Chester DB7 - I think the power is probably ok but would be concerned about the rigidity in trying to hog out a hardened ballscrew with a carbide tip. The other problem I see arising is that I have 12x4 ballscrews, which have a root diameter of pretty close to 10mm, and I need to turn them down to 10mm, so I'm never going to get through the hardened section into the soft stuff below, so even carbide turning on a rigid lathe would produce a pretty rough finish
On reading the previous thread on this subject (http://www.mycncuk.com/threads/2057-...ne-ball-screws), it seems to me that I have two viable alternatives.
1. get them ground down with a cylindrical grinder (but that still leaves me with having to get a m8 thread onto the end), and would probably cost a fair bit.
2. drill into the softer core (which I have found that I can do) and shrink fit or loctite an extension which I can them machine to suit
I'm not too keen on trying the annealing route without knowing what type of steel I'm dealing with, though I may try it on a sacrificial end. One ballscrew I got is about 80 mm longer than I need so if I mess up just the tip I can cut it off and try again
I'll have a go this evening and see what happens
Re: How to machine a ball screw
Tom,
I have the same little lathe but have uprated the motor drive electronics. The lathe is good enough for hobby precision ballscrew machining if you use carbide tooling. I have done this.
The other option is to anneal the portion of the screw you wish to machine. Wrap a wet rag around the portion of the screw you do not want to heat. build a little brazing enclosure out of 4-5 bricks, use a brazing torch or a plumbers torch to heat the end. You need to get it cherry red and let it cool at it's own pace. If you do not keep the screw cool, there is a chance it will warp but this can be rectified later too.
Again, I have done this with satisfactory results and the screw machines like mild steel.
Re: How to machine a ball screw
Quote:
Originally Posted by
komatias
Tom,
I have the same little lathe but have uprated the motor drive electronics. The lathe is good enough for hobby precision ballscrew machining if you use carbide tooling. I have done this.
The other option is to anneal the portion of the screw you wish to machine. Wrap a wet rag around the portion of the screw you do not want to heat. build a little brazing enclosure out of 4-5 bricks, use a brazing torch or a plumbers torch to heat the end. You need to get it cherry red and let it cool at it's own pace. If you do not keep the screw cool, there is a chance it will warp but this can be rectified later too.
Again, I have done this with satisfactory results and the screw machines like mild steel.
Interesting on the DB7 electronics upgrade - I'd like to find out a little more about what you've done - but maybe offline. I fitted a cooling fan behind the motor and it can run at fairly low speeds without overheating, so it's at least better than the factory standard.
As to the ballscrew, I will try the annealing trick. I have about 3 inches to play with so even if it goes wrong I can just cut off the bad bit and start again..
As a matter of interest, after annealing, did you cut with carbide or would HSS do ? Reason I ask is that I don't have any carbide tools, but have lots of HSS available.
Re: How to machine a ball screw
I used carbide tooling. When it is properly annealed however you can file the section you heated, so I imagine HSS should be fine.
IT is a good investment to buy some indexable insert tools and a good toolpost for the DB7.
I swapped the motor drive out for a Parker SSD DC drive after the original motor controller blew up literally. It give very good torque at low RPM and is fully adjustable.
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Re: How to machine a ball screw
Quote:
Originally Posted by
komatias
I used carbide tooling. When it is properly annealed however you can file the section you heated, so I imagine HSS should be fine.
IT is a good investment to buy some indexable insert tools and a good toolpost for the DB7.
I swapped the motor drive out for a Parker SSD DC drive after the original motor controller blew up literally. It give very good torque at low RPM and is fully adjustable.
I'm happy to say that after annealing the end of the ballscrew, I was able to cut it with little difficulty with a sharp HSS tool (see photo). Taking a 12mm ballscrew down to 10mm doesn't quite reach the bottom of the thread, but it'll still be fine to fit a bearing. Thanks for allthe good advice.
Now my next challenge is to find somebody near me (West Sussex) with a mill who would be able to help machine the cross-slide of my mill to fit the ball nuts.
