RT2/OMW Radius\Ball turning tool?

[COMachinist]

Hi All.
I just finished making myself an RT2/OMW ball turning tool. I cut the frames out on my CNC Mill( DIY Grizzly G0704), so is within .001 or so, can't seem to figure out the tool bit grind to keep it from chattering so bad the finish is like I used a cold chisel to cut it out. The ball that is on the handle was the first one I made and have made several more trying to get a decent tool to work. So far I have to spend lot of time using a file on the ball in the lathe to get the chatter marks out. Then the ball is under size by a fair amount. I have tried several sizes from 1" to 2" and they all look the same. I know the tool in not the most ridged ball turner, but it is the easiest to us on my compound and cross slide QCTP type. Here are some pix of the frames and the bit grind. The frames are pinned together with 5/16" drill rod and bushed with 932 bronze and reamed +.001 over drill rod size. the frame seams to not have any slop, but can't figure this one out. I can get the bit to cut good in some spots, but not all the way around the ball, either it chatters on the left hemi sphere or the right just can't get it cut good both sides of center.
Thanks for looking.
CH

 

[rgray]

I would guess it's to flexible. Is it Aluminum? I made one like that (much cruder before I had a mill) and I made it from 3/4 steel and made a tee nut that fits the compound. That way the support arm is much thicker and stronger. It's a little more to set up but not bad, just slide the QCTP out, slide the radius tool in, and tighten.

I've been going to make an insert or a new smaller inside swivel piece. Seems I'm always turning a ball that is on the small side of the turners capacity. The bit stick out is also a problem area for chatter. I see yours has a large capacity also and lots of bit extension.
My center piece is not very handy to change if yous is easy to change then maybe make several for different diameters to eliminate the long tool bit.

On mine if I'm doing a half ball the compound is at 45 deg. full ball 90 deg.

 

[Rick Leslie]

That's a good looking tool, but my first guess would be way too much flex. The cutter is expended way out from the turner and the turner itself sits a good ways out from the QCTP holder. I imagine with the combined tolerance in the compound it gives the set-up a good bit of spring.

If you can find a way to support the tool and holder better, you may eliminate most of the chatter.

Also, remember that your surface speed will change dramatically when ball turning, just like facing a piece in the lathe.

 

[chips&more]

In looking at your pics. I see a pretty large distance from the ball turner tool bit to the ball turners support at the QCTP. And starting at the QCTP, it looks like it’s only maybe 1/2” square aluminum? I suspect the chatter is coming from lack of rigidity because of said above instances. Maybe acting like a tuning fork. But please do not give up, your work looks excellent…Good Luck, Dave.

 

[COMachinist]

Hi All
Yep I was thinking the same thing about it not being ridged enough. I got the idea from a tool I saw on YouTube search for "OMW radius ball turner" They had one like this on Ebay and it was just the frames. I kind of barrowed the design from them and just hacked out the frames on the mill. Just the frames are like 80.00 and finshed OMW is 140.00. Worth the effort I think to make my own. I put large radi on the tool for stiffness. The frame is 1/2" 7075 T6 Al. I figured if it worked ok, I would make it out of steel. The little G0704 mill is kind of taxed doing steel though. I looked at the ones that are made from a boring head and based on a boring head, which looks to be a lot more ridged. But cutting those dove tails is not real easy even with a CNC mill. The Boring head turner can't do a concave radius either, which I would like to do sometime. My cross slide is not suited to doing the round flat tool post type, like Steve Bedair's design which is much more robust. I have a T-slot cross slide that needs machining to fit my lathe but that is a long range project, and I need a few balls now. I have watched some of video on ball turners and to my surprise most of them do chatter to some degree. Maybe I'm whining about this, or maybe I expected to much. I'm thinking about putting another set screw to hold the tool bit tighter. It maybe vibrating with just 1 set screw holding it. I made the hole square to use a square 1/4 HSS tool bit. The broach is shop made, so it is not the best either. It works with 1/4" drilled hole but is not a precision fit hole by any means.
Thanks guys.
CH

 

[Reeltor]

I too think you have too much flex that is causing the chatter. If you decide to go back to the drawing board, Holescreek has plans for a ball turning tool that he designed. I don't know if he has it on this site or not. A Google search for Holescreek ball turner will pull up several locations to see the plans.

I've always planned to make a ball turning tool, just haven't gotten around to it.

Mike

 

[Rick Leslie]

Here's the link to Holescreek's ball turner.
http://lepton.com/metal/ball_turner.html

I wouldn't abandon your design just yet. It's a good looking tool. Just needs more rigidity. You could beef up the inside turning arm and cut it for a larger tool. You can also make some sort of outrigger support for the tool to rest on the cross slide at some point. Everything will be anchored while cutting, so this shouldn't present a problem.

 

[COMachinist]

Here's the link to Holescreek's ball turner.
http://lepton.com/metal/ball_turner.html

I wouldn't abandon your design just yet. It's a good looking tool. Just needs more rigidity. You could beef up the inside turning arm and cut it for a larger tool. You can also make some sort of outrigger support for the tool to rest on the cross slide at some point. Everything will be anchored while cutting, so this shouldn't present a problem.

Thanks for the link. That is a very nice tool well designed and thought out. I will be making one like that will work on my lathe sometime in the future. With winter here and the temps below freezing in the shop which is note fulltime heated. I must use the winter time wisely. When I get a day to be in the shop with out having to wear gloves and a coat all day while the shop comes up to a working temp. I can't afford to heat that shop all winter with temps in the low teens at night. I hope to build some solar panels next summer to keep the shop above freezing inside days and store some heat for night. It sure seem like I work harder now than when I was not retired.:rofl:
Thank all
CH