[How-To] Cutting a 90° slot/groove in a 1.5" bar.

Just for fun

Just for fun

Tim Young
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Oct 7, 2020
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I guys, I'm in the process of making a couple of machinist jacks. I'm wondering how to cut the groove in the top part of the jack. I have an idea on how to do it but I'm a little unsure of how exactly I'm going to get it cut in the center.

I have a PM-935 Mill, and my idea is to place a 3" x 1.5" bar in the vice and tilt the head of my mill to 45° and cut the groove. That's about as far as my idea goes. Since the mill head would be tilted, how would I find center? I could measure it out with my calipers and scribe the center line and then just line up the edge of the end mill. At that point move the table up until I get to the depth that I want. I think that would work but it seems a little by guess by golly.

I have included a photo of my drawing; I hope that help.

Screenshot 2022-07-31 222527.jpg
 
mmcmdl said:
I would skip tilting the head and use a 90 degree cutter . Makes it simple . :encourage:
Click to expand...
I'd consider just using a 90 degree chamfer cutter and cutting it 'face up'. Many of us have one of these already :D

IF you have to do this with the head tilted. I'd suggest using a wiggler to edge-find, the point is at least possible to line up in a way the edge finder wont be.
 
The difficult part is locating the centerline of the part relative to the spindle accurately. If accuracy isn't a great concern, it can be done visually. Scribe a line on the centerline of the part. Move the table and the spindle until the edge of the end mill just touches the scribe line. The object is to have the bottom of the cut on a centerline of the part. Were I doing this, I would mount the part in my vise at a 45º angle. Then lowering the cutter by the depth of the vee will offset the cutter by the same amount so the table will be offset by that amount. You will most likely be making multiple passes so I would use multiple offset, matching each downward move by a corresponding table move. They needn't be precise except for the final cleanup pass.

For accurately locating the center line, a tooling ball can be used. It is a precision ball mounted in a precision stud so the location of the center of the ball relative to the center line is accurately known. A hole for the stud is made on the center of the part and the tooling ball is inserted. An edge finder is used to find the center of the ball and the center position is recorded. This establishes the location of the center line relative to the spindle axis to a high degree of accuracy. A little math can then be used to locate tooling positions. Joe Pieczynski has an excellent video on this very subject.
 
A machinist jack is not a precision tool; scribe a line and visually line up the end mill with it. Over thinking is a waste of time; if I was doing the job, I would use a 90 degree cutter as Dave suggested.
 
If you have a 5c square collet block. Hold the part in a collet in the square block. The block can be located in a vee block against a stop and clamped in a vice. Cut a shallow vee with an end mill, flip the block 180 degrees and mill again at the same setting. Adjust Z height until they match and the adjust X + Z axes equally for the vee depth.
The centre can easily be checked in the block with a dowel and dti.
It might be worth cutting another groove at 90 degrees at a smaller size, it may be useful in the future.
 
Thanks for the replies guys.

FOMOGO said:

3/4" Diameter 90°Degree Included Double Angle Cutter HSS Moon Cutter USA: Amazon.com: Industrial & Scientific

3/4" Diameter 90°Degree Included Double Angle Cutter HSS Moon Cutter USA: Amazon.com: Industrial & Scientific
www.amazon.com
Click to expand...

That looks like that is the perfect tool for the job. Thanks for the link.

ErichKeane said:
I'd consider just using a 90 degree chamfer cutter and cutting it 'face up'. Many of us have one of these already :D

IF you have to do this with the head tilted. I'd suggest using a wiggler to edge-find, the point is at least possible to line up in a way the edge finder wont be.
Click to expand...

I just happen to have a 90° chamfer; I may try that since I don't have one of the cutters that Dave linked to.

RJSakowski said:
The difficult part is locating the centerline of the part relative to the spindle accurately. If accuracy isn't a great concern, it can be done visually. Scribe a line on the centerline of the part. Move the table and the spindle until the edge of the end mill just touches the scribe line. The object is to have the bottom of the cut on a centerline of the part. Were I doing this, I would mount the part in my vise at a 45º angle. Then lowering the cutter by the depth of the vee will offset the cutter by the same amount so the table will be offset by that amount. You will most likely be making multiple passes so I would use multiple offset, matching each downward move by a corresponding table move. They needn't be precise except for the final cleanup pass.

For accurately locating the center line, a tooling ball can be used. It is a precision ball mounted in a precision stud so the location of the center of the ball relative to the center line is accurately known. A hole for the stud is made on the center of the part and the tooling ball is inserted. An edge finder is used to find the center of the ball and the center position is recorded. This establishes the location of the center line relative to the spindle axis to a high degree of accuracy. A little math can then be used to locate tooling positions. Joe Pieczynski has an excellent video on this very subject.
Click to expand...

Thanks RJ, I did think of mounting the part in the vice at a 45° angle and doing the cut from there. I was more concerned about cutting the V groove in the center doing that way. Thanks for the explanation on how it is done. I'll have to search Joe Pie's YouTube to see how he does it.

benmychree said:
A machinist jack is not a precision tool; scribe a line and visually line up the end mill with it. Over thinking is a waste of time; if I was doing the job, I would use a 90 degree cutter as Dave suggested.
Click to expand...

I realize it is not a precision part and I know I could cut it and make it good enough for who it's for (me). The tool Dave posted would defiantly be the ticket. I haven't ordered it yet, but it is in my cart.

Parlo said:
If you have a 5c square collet block. Hold the part in a collet in the square block. The block can be located in a vee block against a stop and clamped in a vice. Cut a shallow vee with an end mill, flip the block 180 degrees and mill again at the same setting. Adjust Z height until they match and the adjust X + Z axes equally for the vee depth.
The centre can easily be checked in the block with a dowel and dti.
It might be worth cutting another groove at 90 degrees at a smaller size, it may be useful in the future.
Click to expand...

Thanks for the reply, I don't have any 5C collets. I've been thinking of a smaller groove the other direction.
 
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