[How-To] How do I set diameter?

[DavidR8]

I have a project on the books where I need to cut a 3/4" diameter half-moon shape in the edge of a plate.
I'm planning to use my Criterion boring head to do this but I'm a bit mystified at how to set the diameter on the boring head.
The woodworker in me would just scribe a 3/4" diameter circle on a piece of stock and then adjust the boring head to scribe the same circle.
But this seems a bit crude and not very machinist-like...
Any assistance is appreciated!

 

[Winegrower]

Joe Pie has a great video on setting fly cutter diameters, ought to work for boring bars too.

 

[main_cogg]

A couple of thoughts, do a test hole in a piece of scrap or sneak up on it until a 3/4" rod just fits into the arc.

 

[DavidR8]

Joe Pie has a great video on setting fly cutter diameters, ought to work for boring bars too.

Thanks, I'll have a look for that.

A couple of thoughts, do a test hole in a piece of scrap or sneak up on it until a 3/4" rod just fits into the arc.

Good idea, this would certainly get the diameter spot on.

 

[mmcmdl]

Just pick up ( tram or use edge finder ) the edge of any part . Dial over .375 and insert the boring head . Dial the head out until the cutter contacts the edge and back off a thou or two .

 

[mksj]

Boring heads cannot take big cuts, so you would probably need to do the cuts in increments and there is also the interrupted cutting which is going to cause a lot of vibration. A 3/4" annular cutter you would just need to align the center, and would cut quickly and they are quite accurate diameter wise. You could also cut undersized with a boring head, measure the radius depth/diameter and then advance the cutter using the dial increments. All depends on how accurate the half round needs to be.

 

[DavidR8]

Boring heads cannot take big cuts, so you would probably need to do the cuts in increments and there is also the interrupted cutting which is going to cause a lot of vibration. A 3/4" annular cutter you would just need to align the center, and would cut quickly and they are quite accurate diameter wise. You could also cut undersized with a boring head, measure the radius depth/diameter and then advance the cutter using the dial increments. All depends on how accurate the half round needs to be.

Good idea, I have a set of metric carbide hole saws. Maybe I'll look to see if I have a diameter that's close to 3/4".

 

[JimDawson]

I would plunge with a 3/4'' end mill. Step over a little bit at a time.

 

[DavidR8]

I would plunge with a 3/4'' end mill. Step over a little bit at a time.

My challenge with plunging is that I have a round column mill so to advance the cutter I'd have to unlock the quill which may give me a bunch of chatter
I'll give it a try though as I think I have a 3/4" end mill.

 

[JimDawson]

My challenge with plunging is that I have a round column mill so to advance the cutter I'd have to unlock the quill which may give me a bunch of chatter
I'll give it a try though as I think I have a 3/4" end mill.

You would be plunging with a boring head, not sure I understand the difference.