DCMT vs TCMT inserts for low power mini lathe

I have bought my TCMT 12mm tool holders (individually, not sets) and TCMT110204 inserts from this ebay seller - deanqiang
100% positive feedback, with reasonable prices and delivery time.

I mostly use the Eccentric Engineering Diamond Tool holder (HSS) which has been mentioned on this forum before however I cant comment on suitability for a mini lathe tho.
I leave the TCMT carbide inserts for the tough stuff. Some folk extol the virtues of AL inserts on steel but has not worked well for me - dull and chip easily.
 
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doj53 said:
I have bought my TCMT 12mm tool holders (individually, not sets) and TCMT110204 inserts from this ebay seller - deanqiang
100% positive feedback, with reasonable prices and delivery time.

I mostly use the Eccentric Engineering Diamond Tool holder (HSS) which has been mentioned on this forum before however I cant comment on suitability for a mini lathe tho.
I leave the TCMT carbide inserts for the tough stuff. Some folk extol the virtues of AL inserts on steel but has not worked well for me - dull and chip easily.
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Seems like that ebay seller doesn't have much for sale right now.

But that Eccentric Engineering tool holder is pretty awesome. It makes grinding easier. I'll look into using more HSS and maybe I'll learn to love it over time. But I'll still keep carbide around for when I'm feeling lazy.
 
Mach_Zero, the guys are right. On a little 7X lathe, HSS is a better choice over inserts. Don't get me wrong. Inserts will work but you just don't have the power, speed or rigidity to take advantage of it. You will need to take lighter depths of cut and will need to be much more adept at using inserts to make them work well.

HSS, on the other hand, is far easier to use. It will typically cut much deeper than inserts will on your lathe. It will also cut more accurately and finish much finer vs carbide at the speeds your lathe is capable of.

Trust me when I say that those of us who suggest HSS have very good reasons for it.
 
Tool pressure is a function of depth of cut and sharpness of the insert cutting edge. Depth of cut should be at least 1/2 the nose radius to get a decent surface finish. So if you do plan to use inserts, a 1/128th" nose radius will let you take shallower depths of cut. To get a sharp cutting edge, you'd specify the tightest tolerance for the insert, so with a DCxT insert geometry, that means you'd be after a DCGT, not a DCMT. A DCGT will typically have a honed sharp cutting edge. So with a DCGT21.50 insert you'd have a sharp cutting edge and a 0.008" nose radius for instance, and you could take passes with a 0.004" depth of cut lowering the demands on your mini lathe. Example: https://www.mscdirect.com/browse/tnpla/45200656

You could also do the same with your existing triangular insert toolholder. Here is an insert for that with a sharp cutting edge and 1/128th nose radius if you wanted to run an experiment. https://www.mscdirect.com/product/details/62576665

But like the others have said, you are probably better off with your mini lathe with HSS.
 
This is just what works for me. When grinding HSS I like to hone the surfaces with a hard Arkansas or diamond stone. The cutting face as well as the relief surface(s) get honed. I think it not only makes the tool sharper but it leaves a smoother finish on the workpiece.
 
The advice above is good stuff. Now to throw in the final cautions and modifiers.

The two key modifiers are rigidity and power. Not all of the mini lathes have the same power. Models like the Little Machine Shop 7350 have a bit more motor than some of it's brethren.

Rigidity can be enhanced with many upgrade kits or modification. Going with the brass gib kits allow the gibs to be tightened just a bit more than the factory steel gibs, which eliminates some of the slop. Going with a tapered bearing upgrade in the head stock reduces some of the chuck play as well. Replacing the compound with a block of steel further increases rigidity (at the cost of losing the ability to do tapers and handicapping threading). And yes, going with the 0XA sized quick-change tool post allows you to use 12mm, 1/2 inch tools, which are more rigid than 3/8 inch tools.

Virtually everyone who has had a 7 by 12/14/16 lathe will admit it is a platform/kit which is upgraded to make it the machine you want. This is even true of "deluxe models".
 
addertooth said:
Replacing the compound with a block of steel further increases rigidity (at the cost of losing the ability to do tapers and handicapping threading).
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At the thread pitches realistically done on a 7x14 there is no need to do the 29degree thing, esp. when using the carbide threading inserts. These are meant to cut straight in on CNC machines. Sandvik has a super handy depth/cut chart to keep you within low loads.

I put a solid post on my 1022 and single point thread all the time. Last 29degree work was in shop class in 1963. You do lose the taper turning capability unfortunately. For 45 and 60dg chamfers I grind HSS tools and keep them in their own QCTP holder.

Gerrit
 
Mach_Zero said:
That's weird. I thought I found the seller and it was showing only 12 items listed. Must have gone to the wrong place. Thanks!
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That usually happens when they don't ship to your location. I get that frequently with sellers in US who won't do international shipping.

Gerrit
 
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