Re: Those Cheap Diamond Inserts

On 7/28/2024 4:45 PM, Bob La Londe wrote:

I was struggling trying to face some big 304 stainless mold inserts to length.  1.5" diameter & 1.375" length.  Saw cut of course.  Parting these off is an exercise in frustration.
 For most stainless work I hand sharpen HSS Cobalt bits, but I was struggling with my facing tool and to get decent finish would have to touch it up after ever pass.  I guess I could move the grinder over by the lathe (cringe) and set a diamond bench stone on the tool cart, but it was rough.
 Now as some of you know a lot of mini lathe users swear by those little 21.51 or 21.52 DCMT diamond inserts.  I had one tool with one in a tool holder and I tried it because nothing else was working for me.  I finished both ends with a single pass on each end of the last six parts with one insert that looks the same when I finished as when I started. After I finished I started going through my box looking to see how many spares I had.  Ummm. Zero.  There were two broken ones on the head stock, but no spares.
 The finish is decent.  I just bought some more that are listed as alloy/stainless.  Also another turning tool, and a boring bar that uses them as well.  I almost bought a through coolant solid carbide boring bar too, but that will have to wait until the next job comes in the shop.
 I don't even think I was using it right.  It was a right hand turning tool and I was just face/plunging it into the saw cut end pushing a cone off the middle as it finish.  I was amazed at how well it worked with such an aggressive cut and no chatter.  I even considered turning up the speed.
 

Its one of those things.  You never see the big boys using those tiny inserts.  They always have these expensive inserts on giant tools that make chips that hit the floor with a clank.  I don't have a giant lathe, but it does weigh a ton (2000lbs).  Its only 3HP, but being a gear head its putting out its full real power (whatever that is) at any speed.  I should be able to take a decent chip and not blow up inserts.  To be fair the lathe does have a coolant system, but I never use it due to the mess.  I tend towards cutting oil.
I know those little bitty inserts work on mini lathes, but I never really used them much on the PM14x40 except where needed to cut a back clearance or something like that.  I should know better.  They made a bigger depth of cut and bigger feed per rev than other things and there was less heat build up in the part.  No coolant.  Just a few drops of cutting oil.
I'm going to quit pretending I have a big boy lathe and just go back to everything I learned on the mini lathe that worked.
P.S.  While I do not recommend them I made a lot of parts on the mini lathe including paid parts.  Not just brass or aluminum either.
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Bob La Londe
CNC Molds N Stuff
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