Torx or Hex screw size for indexable cutters

Pmedic828

Pmedic828

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I am working on a project to convert chipped cemented carbide 1/2 x 1/2 inch lathe bits to index cutters. I purchased some generic triangle inserts and am attempting to make a couple of index able tool bits. Does anyone know what size screw fits the hole in these small cutters. I looks like it could be a 4-40 or something like it. Does anyone know for sure?
 
I would try to use whatever fit the tightest in the hole in the bit if I could. That will help with making the bit and tool repeatable. Also it you go too small it will concentrate the cutting stress on the edge of the hole in the insert and cause them to chip and break very easily. Sorry I don't have a sample to measure, but Mc Master usually has all of those tiny screws in stock most of the time.

Bob
 
I've made indexable cutter holders out of key steel and used modified 3mm or 4mm hi-tensile (Grade 12.8 preferably) Allen headed cap screws to retain the insert. Modified them by cutting a countersink (angle <90 but not important as it bears on hole in the insert but the steeper it is the greater the holding power) on the underside of the head and then drilling/tapping the hole in the holder 0.1-0.2mm toward the wall of the holder that the insert butts against so that the countersink pulls the insert hard against the wall, and presumably the screw bends a little but not permanently if its within elastic limit.
I'd definitely use Torx hi tensile cap screws as Allen heads and keys both wear in use.
Doing it this way ensures that you match what your making not taking a guess that someone else's holding screw will do what you want.
 
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Often times where you purchase the inserts they will have the screws for them.
You could also order replacement screws for a holder from a supplier.
Here in town by me in the detroit area there are lots of tool suppliers and I can just go and get what I need.
I use a small carbide cutter for wood woorking tools that I make and the cutter is about 3/8" round and it uses a 4-40 screw, very small, some of the larger cutters use a 8-32 screw.
Allen heads work fine, torx would work too, grease the threads when you put them in.
 
I would suggest torx. More surface area that hex.

Buy them in bulk and include one with those fine wood turning tools you make.
 
Jeff in Pa said:
I would suggest torx. More surface area that hex.

Buy them in bulk and include one with those fine wood turning tools you make.
Click to expand...
Yup I like the torx too but the cutters that I supply with the tools come with a screw and it's just an 4-40 machine screw with a 1/8" allen head.
 
To get better rigidity than anything commercial ,a shiplike holder for CCMT 09 inserts was made shown on first picture.
The holding down screws for the two active inserts were original from SECO.
Expensive I would say.


Newest version (finished today) has a 4mm /0.7 standard thread under a swiss and expensive Torx 15 head.Left on second picture.


The rigth hand screw is made from a nondescript screw from a closed windov factory.These screws have a funny surface treating like zinc that disapears first time screwing hard.The rigth hand ,selfmodified Torx screw has kept up very well during some very heavy ,nasty interrupted cuts.

I am not paying SECO kings ransoms anymore.

Boxford komp.jpg IMG_1147.JPG
 
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