Dividing Head as a Lathe Substitute

mpoore · Oct 16, 2019

Can a dividing head be used to accurately turn a piece down using a face mill and manually turning dividing head during the cut?

It sounds silly, but my options are limited. My lathe is small and can't handle the piece in question. My new dividing head has a 3 jaw chuck large enough to mount the work piece. It seems like it would work, but I could be missing something. If I can knock off a 1/4 inch, I think I can mount it in the lathe to finish the job.

MP

PocoLoco · Oct 16, 2019

Give it a try, i think it would work.

janvanruth · Oct 17, 2019

mpoore said:
Can a dividing head be used to accurately turn a piece down using a face mill and manually turning dividing head during the cut?

It sounds silly, but my options are limited. My lathe is small and can't handle the piece in question. My new dividing head has a 3 jaw chuck large enough to mount the work piece. It seems like it would work, but I could be missing something. If I can knock off a 1/4 inch, I think I can mount it in the lathe to finish the job.

MP

sure it can, just take your time and be sure the workpiece is secured well and the dividing head also

steve45 · Oct 17, 2019

Sure!

Here's a part I made on a rotary table that was just a little too large to do on my lathe.

Notice the groove around the outside that was also cut on the mill.

johnoder · Oct 17, 2019

Kinda slow - FORTY turns of crank to get one rev of workpiece

Do pay attention to the fact that if the chuck is threaded on, the mill can unscrew it - depends on how you are cutting on it

kenton · Oct 17, 2019

Be aware that a face mill only cuts on the perimeter so you can't park it over the centerline of the dividing head and expect it to cut much. Also using a round tool off center will give you a "hollow cut" as in you won't end up with a true cylinder.

mpoore · Oct 17, 2019

Thanks for the feedback. Sometimes a person that has a little experience is more dangerous than a true beginner because he thinks he knows more than he really does. I was afraid that might have been the case here. My plan might still not have worked without your tips such as the right mill to use and the direction of cut to avoid unscrewing the face plate.

Out of curiosity, has anyone ever tried to true a brake rotor on a RT? Seems like a very viable option.

MP

Bill D · Oct 17, 2019

When the turned the 120 inch magnet coils for a cyclotron at Berkeley they had to flatten the face. So they mounted it to a surplus destroyer? gun mount and rotated it slowly under a bridgeport attached to the ceiling framework.

opscimc · Oct 17, 2019

kenton said:
Also using a round tool off center will give you a "hollow cut" as in you won't end up with a true cylinder.

Can you explain why this would be the case? Why wouldn't a vertical, round tool that is cutting on its edge (e.g. an end mill) create a true cylinder in a part that is mounted horizontally on a rotary table that is off center?

metlcutr55 · Oct 17, 2019

consider using a variable speed drill with adapter to spin the head?

mpoore · Oct 17, 2019

metlcutr55 said:
consider using a variable speed drill with adapter to spin the head?

Another great tip. Thanks.

EPAIII · Oct 17, 2019

If the RT is mounted horizontally (It's axis is vertical) then there should be no problem.

BUT if the RT is mounted vertically (it's axis is HORIZONTAL) then you do want the milling cutter to be directly above it's axis. This may be what Kenton was talking about.

And if the RT is at an odd angle, then heaven help you. You are going to need some real deep geometry there.

opscimc said:
Can you explain why this would be the case? Why wouldn't a vertical, round tool that is cutting on its edge (e.g. an end mill) create a true cylinder in a part that is mounted horizontally on a rotary table that is off center?

opscimc · Oct 17, 2019

EPAIII said:
BUT if the RT is mounted vertically (it's axis is HORIZONTAL) then you do want the milling cutter to be directly above it's axis.

In this circumstance the milling cutter would be doing its cutting only on one side of the cutter so would quite clearly not remove material evenly unless the table was moved back and forth parallel to the rotation axis of the rotary table. In which case it also would produce a cylinder.

kenton · Oct 17, 2019

opscimc said:
In this circumstance the milling cutter would be doing its cutting only on one side of the cutter so would quite clearly not remove material evenly unless the table was moved back and forth parallel to the rotation axis of the rotary table. In which case it also would produce a cylinder.

I saw dividing head and imagined using it with the axis horizontal, with the axis vertical no problem. As to running the tool back and forth, you could certainly do that but you will either end up spending a shit-ton of time milling 360 +/- passes and get something very cylinder like or spend a lot of time and accept that your part is a polygon and not a cylinder.

PocoLoco · Oct 17, 2019

Out of curiosity, has anyone ever tried to true a brake rotor on a RT? Seems like a very viable option.
No, but I have ground them on a flywheel grinder. Parallelism is the tough part. I run a file across the top part where the wheel fits against, just to make sure it is flat. Then put that side down on the table, secure and grind the inside surface. Flip and grind the outside. Never make any money on it with autozone doing them for $9, and new ones for $20. I only do odd ones that are high priced or unavailable. Or my own on a day when no one is open. The hot ticket is the spindle from a junk brake lathe. Mount it in your engine lathe and turn rotors, or anything with a concentric hole. Takes up less room than another machine, and cheap.

strokersix · Oct 17, 2019

Turning rotors: Stand up an extra spindle on your mill table to hold the rotor on its own bearings. Run a vee belt around the perimeter and power with a motor to spin the rotor. Then traverse a single point tool to true the surfaces.

I've done this with unobtainable rotors for vintage vehicles. No way I'd bother on something that can be easily purchased.

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