The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)

[hermetic]

Another great save Andrew!

[mattinker]

I've always been a bit jealous of your EDM machine!

Cheers, Matthew

[awemawson]

It's saved my bacon several times Matthew 

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!

[awemawson]

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

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.

[awemawson]

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   

So what's left

Just the taper profile for the A2-5 chuck to fit on, and also make a driving peg for it.

[awemawson]

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 

. . . 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.

[WeldingRod]

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

[awemawson]

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 !

[awemawson]

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 

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 

First the worn tip:

Then a virgin tip:

[awemawson]

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!

[awemawson]

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

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)

[jiihoo]

It is definitely looking better with the 2nd insert!

[awemawson]

Oh yes Jari - and I've tried a few random ones today  !

Today's job was to see if there was any way to cut an undercut at the root of the taper where it meets the body of the adaptor. This is to prevent any problems mating with the chuck body. Chuck body has a very small (just over 1 mm) 45 degree facet here but with the tips I have I can't get the root radius small enough to sit in that facet.

Normally I'd just use a parting tool or diamond tipped tool to form a groove at the root, but here I am working out side of the envelope where normal tools can reach.

Trying to push the TPKN 1603PPTR to it's limits to make a groove there I ended up with a nasty crash, pulling the EN8 bar end out of the chuck  Lucky this is an experimental test piece! Tidying it up on the manual lathe I got it back to a state where I could experiment cutting ever smaller tapers I've come to the conclusion the with a TPUN160304 tip (ie 0.4 mm tip radius) I should be able to get away with it - I have TPUN160308 tips but in a carbide grade suited to aluminium - so too soft and too large a radius.

TPUN160304 tips on order in P40 grade (steel and alloy steels)


All a bit of a pain but this is why I'm making numerous experiments before working on the adaptor itself - don't want to wreck that at this stage

[nrml]

Can't you do the undercut on the manual lathe at the end? It shouldn't affect the mating of the chuck to the adapter.

[awemawson]

Thanks for the suggestion.

The face where the under cut should be has to contact the relevant bit of the chuck absolutely and precisely when the tapers close together.

As the taper wont close without the under cut I cannot be sure the sizes are right, and dismounting it would be counter productive concentricity wise,

I had already thought that I could 'half machine' the taper, mount it on the manual lathe for undercutting, remount it on the CNC and finish the taper but it's fraught with introduced inaccuracies

 . . . .it's all a  blooming palaver !

[nrml]

Ahh. I learnt something new there. I always believed that it was the taper that was the important bit and that the undercut was just relief to ensure it sits flush.

[awemawson]

I have to get three features to all come together at the same time. The male and female taper, the adaptor to spindle flange (with perhaps a few tens of microns gap to pull the taper firmly together ) and the inner face where the hydraulic ports are. Again these can have the odd tens of microns gap as there are O rings squashed here to seal the ports.

[modeng200023]

Andrew, with this high accuracy that you are working to does temperature of the mating items become important?
No doubt you have this in mind but I've not seen temperature mentioned in this discussion.

John

[awemawson]

It does John but fortunately everything is being kept in the same environment. It was surprisingly significant when I was grinding the taper gauge and measuring how far it penetrated  the female taper in the chuck. Seating tapers is a funny old business, a little goes a long way, and over shooting is only too easy!

I think the major issue is to get the taper to seat leaving just a nat's thing-a-me-bob of clearance between the chuck and it's flange, so when the bolts are torqued down the taper is pulled well home. The internal mating faces where the hydraulic ports join is marginally less critical due to the aforementioned O rings giving a bit of tolerance.

I'm pleased to say with the larger taper of the 'adaptor to lathe spindle interface', once bolted up, and then unbolted, it took a few persuasive blows from a large rubber dead blow hammer to unseat it  and it's that sort of fit I want to achieve with the 'adaptor to collet chuck interface'

(A self releasing taper needs to be 16 degrees or greater - this one is 2 x 7.125 = 14.25 degrees so just on the self holding side of the line!)

[awemawson]

Can't get much done today due to other commitments,  however I spent some time trying to convince myself that using the 0.4 mm radius tips that are on order will produce a tight enough fillet at that pesky corner to be accommodated by the existing chamfer on the collet chuck.

. . . I think that it will but would welcome comments as usual.

I measured the chuck chamfer as reasonably accurately as I could visually at 1.5 mm, and assumed (!) that it was evenly distributed either side of the centre line of the chuck face and taper wall, which are at 97.125 degrees to each other, and drew it up, large scale, in Autocad. It seems to say I'm OK but as I say comments are welcomed!

[djc]

Since you mention "the chuck" in a singular fashion, is it only one, specific chuck you want to mount on the adaptor?

If so, is there any reason not to modify (increase) the chamfer on the chuck if the peskiness proves to be obstinate?

[awemawson]

Thanks for the suggestion - not one I'd considered, however apart from not being able to mount it in reverse and it being hardened steel no reason at all 

I'm hoping such activity will not be needed, but yes this is to mount a specific internally hydraulically operated collet chuck of A2-5 mounting specification on a spindle made for A2-6 devices with the same internally operated hydraulic mechanism.

(most CNC hydraulic chucks use an external hydraulic co-axial cylinder mounted round the spindle bore tube - not this one!)

[awemawson]

The postman brought the new 0.4 mm carbide tips this morning - not due until Monday so this is a bonus!

They are TPUN 160304 S6-P40 , so the correct grade of carbide as well as correct tip radius which has made a noticeable difference to the surface finish as well as to the corner radius.

I now need to be brave and mount up the actual adaptor and work on that 

[mattinker]

It's the kind of thing that if your doing it for yourself is not the same doing it for someone else!

All the best, Matthew

[awemawson]

The EN8 billet that I have been testing on had a feature that I'd turned on the opposite end that I'd intended for a final 'to exact size' trial from which I could take precise tool positions using the CNC lathes positioning system to avoid any tool setting errors. So I mounted it up, the first operation being to face the end and face the shoulder to the exact 14.270 mm depth. Initially all went well then another DISASTER - tool dig in and part ripped from the chuck 

Initially this greatly puzzled me - I was using very conservative in feeds, but then it dawned on me - this boring bar mounts it's insert with ZERO back clearance behind the cutting edge. Usually there is a good 5 or 7 degree, so as the insert is fed in radially if there is ANY vibration it ends up taking a broader and broader cut. The evidence was there from the last dig in. If you look back to the picture of the damage look how broad the eventual chip was once the tool had dug in 

Now I cannot afford to risk  this when turning the actual adaptor - I've invested too many hours in it, so I've decided to change horses mid race. I've found a 32 mm boring bar of suitable length that takes VCMT 1604004 tips with a 35 degree diamond profile mounted to give very adequate  clearances so I'll just have to twiddle my thumbs until it arrives.

. . . such is life . . .