Thread: Cutting a rack on the mill

Michael it sounds like you have a HM50-52 or similar? I have a Bridgeport style mill on steroids (3hp) and a horizontal head for it, which I am pretty sure I can setup so that the cutter is at 90 degrees to the x axis.
I have a job to do with it in the next few days so I will have a look, actually reading your post made me work out how to do my job- I am making some jaws for my cnc vice so I can hold six 1/2 inch hex bars for drilling and tapping, provided I have a suitable cutter I will just put v grooves in at a set distance apart, that distance will be the X axis movement between holes.
Will

Michael,
Do you have a shaper.

Phil

Can't be done without a rack cutting attachment for a horizontal mill or a very, very big diameter cutter (run at appropriately low speed) using a vertical head slewed 90 deg. I've tried.

I used a shaper. Don't have the time, bandwidth etc to go into details.

PDW

I have a mill with a horizontal spindle that has a vertical head on it - it's somewhere in the "show us your mill thread I think".
I do have a shaper and it could be done on that although there is the indexing to think about there too.

Michael

Just searched on rack cutting attachment - Yep. That looks something that would do the job (damn. Another thing for the list)

... back in '41. I don't know if these images are of any use to you Michael.

BT

> Any other thoughts?

Maybe this?
Fly Cutting a rack for a 36 DP pinion gear - YouTube

Fly cutting vertically could be one way around the issue but would need a decent support behind the rack if done vertically. Something to think about anyway.

I think though that Bob gets the elephant stamp (or would do if Bryan hadn't used the last one!). The pictures of the indexing mechanism that he has posted show how it can be done. I need to sit down and work out how DP (probably via CP) would relate to driving ratios. I may be able to drive back through the dividing head which would save yet anther thing taking up space in the shed. More thinking...

Michael

Originally Posted by Michael G

I have a mill with a horizontal spindle that has a vertical head on it - it's somewhere in the "show us your mill thread I think".
I do have a shaper and it could be done on that although there is the indexing to think about there too.

Michael

Just searched on rack cutting attachment - Yep. That looks something that would do the job (damn. Another thing for the list)

Std bought rack cutter diameter is too small to use with a swivelled vertical head. Measure the distance from spindle c/l to outside of head & see what you get. Your cutter needs to be 2X this distance plus DOC to be useful. Now can you swing a cutter that you've had to make at slow enough speed not to burn it up?

Shaper with DRO works fine. Slow, but fine.

Having done this my suggestion is, buy a length of rack and move on. I don't think I'd bother doing it again.

PDW

Originally Posted by Michael G

Fly cutting vertically could be one way around the issue but would need a decent support behind the rack if done vertically. Something to think about anyway.
Michael

Michael,

For short sections of rack this should be quite doable, though tedious. The attached photo is obviously not a rack - it is a staple holder for fitting Clipper type steel belt lacing staples - but the work holding and indexing problems are similar. It is some years since I made it, and of course I didn't take any photos of the set-up, but I don't remember any problems. The workpiece is 50mm long, 25mm wide and 10mm deep, and the slots for the staples were cut on an RF30 mill drill with a 1.5mm slitting saw. As far as I remember, I just held the workpiece vertically in the vyce. I don't remember using a dial indicator for indexing, but may have done so. I suspect I probably relied on the quill feed dial though, which might not be accurate enough for a rack. With this length there was no problem with machine rigidity using the slitting saw, and I could probably have cut a 75mm long holder if it had been necessary without trouble. I think a 100mm workpiece would probably have been getting close to the RF30's rigidity limits though.

If you did decide to go this way, it might make life easier if you made an initial series of cuts with an appropriately sized slitting saw first to remove some excess metal, before producing the final tooth depth and shape with the fly cutter.

Frank.

I recall seeing a thread elsewhere about this. Apparently rack tooth flanks are straight, so you only need a simple slot drill ground to your pressure angle. Or cut each flank individually using vertical head tilted with a standard end mill

Greg Q

Originally Posted by Greg Q

I recall seeing a thread elsewhere about this. Apparently rack tooth flanks are straight, so you only need a simple slot drill ground to your pressure angle. Or cut each flank individually using vertical head tilted with a standard end mill

Greg Q

Thank you for pointing out the obvious! The slot drill ground to the pressure angle for the rack is a tip well worth remembering, and would allow you to cut reasonable length racks on almost any vertical milling machine. I have heard this mentioned before, and had completely forgotten it.

Frank.

Originally Posted by Greg Q

I recall seeing a thread elsewhere about this. Apparently rack tooth flanks are straight, so you only need a simple slot drill ground to your pressure angle. Or cut each flank individually using vertical head tilted with a standard end mill

Greg Q

Yeah, I thought about that when I did mine. For racks with a reasonably large DP, it would be a good way to go. For small stuff, I can see going through a lot of cutters. No thanks.

Better to (re)design around what you can buy. Some challenges are better circumvented than solved.

PDW