I am building a ball turning attachment for my lathe and going to use a carbide insert. I am about to drill the tool bit to accept the insert however I am in a quandary as to what size drill and tap to use to secure the insert. The insert is a TNMG (Triangle/Negative Rake) with an attachment hole size of .140". :thinking: Any assistance would be appreciated.
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What Size Drill and Tap To Use?
- Thread starter ML_Woy
- Start date
Your best bet is to measure the screw you will be using. The only one I've done was metric - M4x0.7. I'd expect any screws available in your area would be SAE. Best to measure, then follow the charts.
I would recommend picking up a HSS tap. The ones that come with most sets are carbon steel and easily broken , especially in the smaller sizes.
I would recommend picking up a HSS tap. The ones that come with most sets are carbon steel and easily broken , especially in the smaller sizes.
For my T insert (3/8" IC) tool holders I used 6-32 x 1/2 wall plate screws. The countersink on the insert is a near perfect match to the screw... Granted those Iscar (and the like) screws are much better, but they're expensive and hard to find.
Easy to see here:
A bit harder to see here:
The screw hole was intentionally set about 0.005 back to force the insert into the toolholder.
John
Easy to see here:
A bit harder to see here:
The screw hole was intentionally set about 0.005 back to force the insert into the toolholder.
John
Thanks Gary, for the information, I was not sure what fastener to use, this is just what I needed. To bad I did not post this yesterday morning before I placed my order to ENCO.
Thanks John, for the information, your reply has brought up another question. How much overhang over the front of the tool holder should I allow? How much clearance should there be between the face of the tool holder and the tip of the insert? I know that to much would leave the insert unsupported and to little would cause clearance problems. The top of my tool holder is 3/4" x 1.06" and I was planning on setting two TNMG-321 inserts back to back with a ..125" wall between them.
Am I understanding you to say that the hole drilled in the tool holder is intentionally drilled .005" off center of the hole in the insert to force the insert against the back wall of the tool holder? Isn't that some pretty accurate drilling?
Thanks for the head up on the tap. I read one post a while back where a guy broke three taps before he got his tool completed, that meant two tool holders in the garbage.
Ordered up a couple of those special screws and they arrived yesterday, had to get a tap as well. Once I got them I checked them out with the TNMG carbide insert to see how they fit and found that they were not .160 in diameter to match the hole in the insert, a little to small. So I am still looking for the proper size tap and screw to fit a .160" hole. The good news is I now have a new tap for my collection and four small screws for another project.
