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Well I couldn't leave it at that - could I  :clap:

So out to the workshop and I swapped the insert for a TPKN 1603PPTR which is the one with the odd two facets rather than a  radius.

It actually gave a pretty good, and certainly acceptable, surface finish on this test piece of EN8 steel at 700 RPM. I just need to work out graphically if there are any implications for the male taper nose profile where it protrudes from the base metal - it may be within the chamfer of the chuck, but I need to check that they won't clash.

(The value "BS" in the picture is 1.47 mm)
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It seems that EN19T (or 4140) likes a surface speed range of 131 to 208 m/Sec when turning with carbide. For this taper that works out as speeds between 522 and 831 RPM.

Doing a test turn at 600 RPM with a fresh tip the finish was not as good as before but acceptable. I suspect that previously it was being burnished by the worn tip.

Hopefully finish will improve when I rig up a coolant pipe for this tool.

Even after this minor test there was detectable wear on the tip - I wish I knew what grade of carbide it is. I do have some TPKN 16 03 PP tips in P40 carbide that will fit this bar, though instead of a tip radius they have two small facets approximating a radius - I may try those tomorrow!




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I dismounted the tool holder intending to put it on my off line tool setting rig, but I noticed a tiny flash of light from a facet on the tip.Close examination under a glass revealed a worn facet - so obviously I need to radically address feeds and speeds. Trouble is I have no idea what grade of carbide this is.

After all those dramatic glowing bits of swarf WERE a clue  :ddb:

No point in accurate tool setting until I get this feature sorted - probably just far too high a surface speed added to no coolant.

I tried photographing the tip on my Baty Shadowgraph, but the image was swamped by the light - the only way I could get a result was to make a little video moving round the tip shape - hopefully this will convey what I can see with my eye  :scratch:

First the worn tip:




Then a virgin tip:




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So this morning I set up an EN8 test sample to see what surface finish I can achieve and what chatter I can see if any.

Sweet spot seems to be 1500 rpm with 25 micron DOC - not using coolant so the whispy swarf glows like steel wool falling onto battery terminals!

Finish should improve with coolant. Note that this taper is the correct 7.125 degrees wall angle but smaller diameter than the actual adaptor nose as this bit of EN8 has been turned a few times !





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New from Old / Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Last post by WeldingRod on June 22, 2021, 02:31:48 PM »
If you make a shrink on sleeve you could stiffen that bar.  Or, a really close fit with oil could provide a nice damper.  If you go for the latter, dont forget to lock it axially!
Just dreamin' ;-)


Sent from my SM-G892A using Tapatalk

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New from Old / Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Last post by awemawson on June 22, 2021, 09:23:36 AM »
Nothing for it then but to grit my teeth and take the angle grinder to that nice boring bar. This is of course sacrilege

Very carefully working out  how long to leave it I then did the deed, and cleaned it up on the disk sander to at least look presentable. Mounting the shortened tool in the turret it at least looks less ridiculous than before it was cut, but how will it perform  :scratch:

. . . Well the answer is with FAR less vibration - it might actually be satisfactory. I've only tried turning under what is called 'Overstore' on this controller, where you can set the spindle rotating at your desired speed and direction, then use the manual jog or handwheel to control Z and X

Have other duties this afternoon so next time I'll try under program control and see how good a finish I can achieve.
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New from Old / Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Last post by awemawson on June 22, 2021, 07:00:46 AM »
I'm delighted to say the postman brought the long series 6 mm cobalt drills a day ahead of schedule, so I was able to press on and finish the last hydraulic oil gallery.

I must say that these M42 8% Cobalt Osborn drills make short work of this hard alloy steel.

Same process as before culminating in tapping for an 8 mm grub screw as a stopper and cleaning up with a countersink. It is a huge relief to have finished these long holes    :ddb:

So what's left :scratch:

Just the taper profile for the A2-5 chuck to fit on, and also make a driving peg for it.
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New from Old / Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Last post by awemawson on June 21, 2021, 02:19:53 PM »
Ade's kind gift of the sacrificial boring bar arrived this afternoon.

Same 32 mm diameter as mine but somewhat longer - glad to find that I have suitable tips in my stash of carbide :thumbup:

I gave it a bit of a clean up on the wire wheel and mounted it in a 32 mm VDI40 socket holder - note the the socket supports the bar for  85 mm and that I calculate that I need about 200 mm total length so I can shorten this one by about 175 mm.

Just for a laugh I mounted it up 'uncut', and naturally it vibrates like a goodun - we'll see what happens when shortened. If it still vibrates I'm going to surround it by a  cast lead jacket, but that's for tomorrow.

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New from Old / Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Last post by awemawson on June 20, 2021, 10:48:33 AM »
It's saved my bacon several times Matthew  :ddb:

So after lunch I cleaned up the entry to the first oil gallery with a suitably sized countersink, and then re-set the mounting to present the other two oil ports vertically above each other. I'm glad I went to the trouble of making that pivot, it makes life so much easier!

Then it was a case of 6 mm end mill to give a start for the drill on the curved surface, and drill it out to 52 mm deep with a short series HSS Cobalt drill.

The hole needs to be about 110 mm deep finally but I've gone as far as a short series is happy, and that with masses of ups and downs for chip clearance and adding lubrication. Long series cobalt drill is due by Wednesday and although I have several plain HSS ones, in light of the previous experience I'll wait until it comes!

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New from Old / Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Last post by mattinker on June 20, 2021, 10:38:22 AM »
I've always been a bit jealous of your EDM machine!

Cheers, Matthew
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