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What left hand boring bar and inserts for reverse helix right hand internal threading?
- Thread starter 9t8z28
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- Jun 12, 2014
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I was ordering some Carmex 16 IR AG60 inserts and was reviewing their online information. If one is using lay down inserts evidently their are differences between both internal and external inserts as well as the holders. So although an ER insert may work in an IR tooling, it imay not be ideal, this may be manufacturer specific. A common problem with any insert threading tooling is the minimum diameter, even with an 11 IR A60 the minimum internal diameter one can thread is about 5/8".
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If the OP is still pursuing that bar, then, he'll need ER inserts. If you look at the bar, it has a flat and the seating portion of the insert appears to be at at 7 degree (or more) angle. If he used a Carmex IR insert that would give him about a 20 degree positive face angle which is far too aggressive. It would put excessive pressure even with light cuts and bend the bar way too much. This is specifically why I recommended an ER for that bar.
I have about 2 dozen different threading bars and holders (actually, probably more than that). At times, I've probably used the "wrong" carmex insert as per their recommendations. I've probably used "normal" inserts in Carmex bars.... For many years, I always did threading with hand-ground HSS. About 10 years ago, sharpened carbide became readily available. Like all manual machining, you use the tool in the way you best see fit.
Ray
I have about 2 dozen different threading bars and holders (actually, probably more than that). At times, I've probably used the "wrong" carmex insert as per their recommendations. I've probably used "normal" inserts in Carmex bars.... For many years, I always did threading with hand-ground HSS. About 10 years ago, sharpened carbide became readily available. Like all manual machining, you use the tool in the way you best see fit.
Ray
Just giving an update:
I purchased the left- hand bar that I linked to in my opening comment. So far it has worked out great. I just used it to thread an M20x.5 test piece for my Hemingway rotary broach. ( I wanted to practice on scrap before I tried to thread the actual part). I started out with a threaded relieve at the back of the bore. I then set up a stop and threaded in reverse at 650 rpm. I made a mistake while calculating the thread relief and did not go deep enough but the insert did not mind at all and cut without any issues. The threads turned out great and fit my male M20x.5 retainer that I previously made.
Some were commenting that this bar might not work because it was a copy and the bar did not use an anvil/shim to set the insert at the correct angle (positive/negative). That may still be true but the threads turned out excellent for a hobbyiest.
Here is a picture of the ID threads. For some reason at the bottom of the bore the thread crest looks flat but at the side they look sharp. This is the Camera doing this and is giving the appearance that the threads were not cut on the same centerline as the bore. I assure you this is not the case. I should have taken a better picture.
I purchased the left- hand bar that I linked to in my opening comment. So far it has worked out great. I just used it to thread an M20x.5 test piece for my Hemingway rotary broach. ( I wanted to practice on scrap before I tried to thread the actual part). I started out with a threaded relieve at the back of the bore. I then set up a stop and threaded in reverse at 650 rpm. I made a mistake while calculating the thread relief and did not go deep enough but the insert did not mind at all and cut without any issues. The threads turned out great and fit my male M20x.5 retainer that I previously made.
Some were commenting that this bar might not work because it was a copy and the bar did not use an anvil/shim to set the insert at the correct angle (positive/negative). That may still be true but the threads turned out excellent for a hobbyiest.
Here is a picture of the ID threads. For some reason at the bottom of the bore the thread crest looks flat but at the side they look sharp. This is the Camera doing this and is giving the appearance that the threads were not cut on the same centerline as the bore. I assure you this is not the case. I should have taken a better picture.
Hi, would you mind sharing where you get this pic?
I didn't post the pic but I believe its from the Carmex website.
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I've never seen inserts used to cut on the trailing edge - away from the chuck. There is no clearance on the trailing edge as they are tilted the wrong way in the toolholder. Threading away from the chuck looks cool, but not for insert tooling.
Left hand and right hand bars are commercially available with the appropriate inserts for threading in all directions for left hand and right hand threads
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- Feb 21, 2022
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I haven't looked into what is now available, I do know that left hand and right hand threads whether internal or external can be produced cutting towards the chuck but with the rotation reversed, always on the leading edge of the insert.
Tip: If I have to cut an external left hand thread, I use my standard right hand boring bar on the o/d up side down, towards the chuck in reverse.