Large Indexable Insert Holder and Small Lathe

[RonGinger]

How did you cut that slot in a tool holder? I was given a 3/4" holder once and tried to cut it down to fit my toolpost. The thing was as hard as glass and the only way I could cut it was with an angle grinder, then finish it on a surface grinder. It just ate up a HSS end mill.

 

[kquiggle]

I can't speak for MachineTom, but when I whittled down my insert holder I used a carbide end mill and took light cuts (and it threw off some wicked looking purple chips).

 

[Swifty]

I've also machined down some insert holders, I used an inserted tip end mill. The holders are very hard, but carbide cutters work well on them.

Paul.

 

[MachineTom]

KQ, A TNMG insert was an incorrect choice for your use. The letters and numbers on an insert tell you what it is. So in this case the second letter tells you the relief angle, and in this case the N stands for NADA, so a zero angle would need the relief to be in the tool holders that makes a negative tool angle. Almost as common as N angle inserts are P angle, Yes call it Positive. Those N inserts may work great on brass, but for steel low speed machines, P with a chipbreaker groove is the ticket.Look up Carbide Inserts, That will provide the key to figuring out what is what with inserts.

The pocket was milled with HSS bit the mount with carbide to make the opening, and HSS on the 60° cutter. I cut off the old need with regular bi-metal blade in the bandsaw. Those a Kennametal holders not some no-name stuff. Drilled and tapped with HSS. When I drll these a fresh grind is always done first, why, the material will work harden very easily, thats why I cut the machined end off. The first time I tried to do this was a learning experience. Now its all old news.

In my case these holders are used for special inserts. Today I just finished a Left hand Top Notch type Holder for ACME threading I need to do. Each cut is shallow so the loads are not that high. I don't use these for regular cutting as area to mount to the tool post is not that large.

I the case of someone with a small lathe an inch or larger holder is similar in size to the regular QCTP holder.

 

[mu38&Bg#]

Tom, he has a negative holder which give the proper relief angle with a 0° (N) relief angle insert. In fact, MTGNR holder in Dorian give a 7° relief with this kind of insert. An insert could be sourced with enough top rake to give the geometry desired even mounted in that holder. One problem with this holder is 0° lead angle, cross cutting depth of cut should be less than nose radius.

TNMG doesn't fully describe the insert and it could have been a roughing insert for all we know. 222 gives it a fairly large nose radius for a small lathe. What is the make and grade for said insert? With inserts you have to be specific.

Greg

 

[wild350x]

I've used TPG style inserts with an adjustable top mounted chip breaker in small lathes with great sucess. We had a Dorian quick change tool post on an 9x24 that came with a set of holders that held that insert. It held one on each end of the holder, one set up for turning and the other for facing. I had one set up for roughing and the other for finishing. It had a hss or toolsteel chip breaker that slid across the top of the insert an was held un place by the clamp. You could also buy HSS as well as carbide inserts for this holder. If you didn't like the angle or nose radius it was easily adjustable on the tool bit grinder or with a good set of carbide sharpening stones. I always liked this setup but most production shops don't as the inserts don't hold up well under extreme loads and only offer 3 cutting edges. As for milling case hardened toolholders you can also use a grinder to remove .030-.050 of the outside material where you are going to machine and the core will be much softer. Old dull ballnose endmills make great spotters to break through this case if you want to drill into one.