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

[awemawson]

I did have a 'heart in the mouth' experience this morning 

I decided to set the spindle running at low revs - 100 rpm just for a first visual check - and it was immediately obvious that something wasn't right. There was a distinct eccentricity of the outer nose where the A2-5 taper will be turned.

Now a few microns of run out at this stage is no issue as the next stage is to use the lathe to turn the next taper, but NOT something that I can see with the naked eye!

Running a feeler gauge around the interface between the spindle nose and the adaptor flange revealed an uneven gap. All 6 M12 bolts good and tight so what's happening. I thought perhaps the 'drive peg' hole wasn't deep enough and it was bottoming.

Unbolting the problem was fairly quickly found - the 6 retaining bolts were very marginally too long and had bottomed in the tapped holes in the spindle, and weren't actually pulling the flange tight onto the spindle 

It was a matter of a few minutes to replace the bolts with shorter ones, and phew - all now looks fine 

A big manual lathe tidy up now and I need to work out how to program the Beaver to give me the 7.125 degree taper in a progressive manner so that again I can creep up on a snug fit and yet be able to see what's happening. (The tool turret gets in the way of visual checks)

[awemawson]

OK Colchester Master 2500 returned to normality after a rigorous clean up and replacement of 3 jaw chuck.

And while this was happening I powered the Crocell pot up so that I could preserve the Taper Test Gauge. After all it took ages to make, might as well look after it, although frankly it's unlikely that I'll use it again.

[mattinker]

If you preserve it it shouldn't be needed again except now I've jinxed it by saying that!  Sorry!!! Cheers!!

[awemawson]

This mornings task - sort out where the O ring seats had been compromised by through drilling the 8.5 mm holes for tapping the A2-5 mounting flange.

First I had to return the O rings seats to their design depth of 2 mm - this had been made shallower by adjusting the taper to fit the gauge. Manual mill, hydraulic ports located by dropping a 6 mm drill into them - 1/2" end mill inserted into collet and depth adjusted accordingly.

Then I turned up some 8.5 mm rod with the tolerance on the fat size, cut a pair of 6 mm long 'pills' to act as inserts, popped them in with Loctite 601 high strength retainer and adjusted their depth with screws coming in from the A2-6 side.

The insert very slightly impinges on the recess for the O ring but I don't think that it is of any consequence (famous last words!)

Can't do much more until the 601 has cured - probably just as well as I have duties with cottage guests arriving.

[awemawson]

The 601 has had a couple of hours to go off - it's supposedly OK after 25 minutes. So I've put O rings on the adaptor and re-fitted it to the spindle - I want to check what sort of squash they take up - I'll leave them over night and examine them tomorrow.

Meanwhile I needed to work out what tool to use to be able to 'get at' the A2-5 taper to machine it. It's well inside the protected zone being 'behind the chuck' so to avoid mucking about with the settings for the 'machining envelope' I'd got hold of a humongous through coolant boring bar with a 32 mm shank. Mounting it up I proved that I could reach all aspects of the taper so next thing to check is the through coolant.

The bar is hollow with a small passageway for coolant. The holder accommodates this and also external coolant through a pipe mounted in a ball socket that can be locked in any position by tightening a countersunk cap head screw that bears on the ball. To redirect the flow down the hollow all I have done is to rotate the ball so that the hole for the pipe is at 90 degrees to where it should be to block the port, it's not 100% but adequate for what I'm doing.

The bar is really sticking out too far but I need it's length to to maintain visibility and I don't want to cut it down as that is the only way of reducing it's projection. (Shorter bar = less chatter but it's pretty solid!)

So two thing left to do, both of which I'm nervous of:

A/ programming the taper so that I can advance it in nibbles for test fits

B/ Drilling those long linking holes to couple the hydraulic ports

[awemawson]

Today's Task: Turn a test billet in EN8 to replicate the A2-5  blank adaptor nose so that I can test my program before unleashing it on the actual adaptor to turn the taper.

So I re-fitted the manual 3 jaw chuck to the CNC lathe, and mounted the 100 mm bar end of EN8 in the manual lathe to reduce 14.31 mm of it to 86 mm.

Oh -what's happened to my nice Newall DRO - none of the value setting buttons would work although the axis values displayed and were updated with movement 

I've had this Newall Topaz two axis DRO on my Colchester for about 20 years - they had a deal whereby the price was greatly reduced AND a man came to fit it, so I parted with quite a wad of cash but it has been excellent apart from one problem that started just after warranty expired: The 'Set Zero' buttons for X & Z didn't work but I could still set zero by entering '0' on the appropriate axis - just an extra key push. Well now I couldn't even do that

I do have a spare 3 axis head but would rather not use it - time to pull the 2 axis one apart taking great care not to tear ribbon cables. Well as expected there's not much that you can do inside. There is a receiver board for the transducers, a power supply, a main logic board, and sandwiched below the membrane keyboard with a ribbon cable connection. Very easy to inflict fatal damage in these things if you are not very careful.

Now I was strongly suspicious of the membrane keyboard itself, but it was bonded to the front panel and removing it wasn't feasible. OK what CAN you do - well the keyboard connector is a ribbon plug in - clean it, put a bit of switch contact cleaner on it and pray  to Mecca.

To my HUGE surprise not only was the fault that developed today cleared, but the one I've been putting up with for decades - it WORKS

OK great excitement but get on with some machining . . . the 100 mm bar end was quickly reduced to 86 mm for 14.31 mm of it's length producing some impressive purple swarf (3 mm DOC at 770 RPM) - don't try and handle this sort of swarf - it will rapidly cut you to the bone. I use long snipe nose pliers.

Bar end now mounted in the CNC lathe and I have an embryo program written to cut the taper but it needs a bit more tweaking when there are less distractions around.

[BillTodd]

I've had to replace the front panel of a couple of topaz Newall dros, although yours looks in better shape than the ones i replaced

Newall dont sell the membrane separately (may not even sell those any more!)  .

Bill

[awemawson]

I noticed that the keyboard unit, which seems to be bonded to the front panel, was made by a firm in Eastliegh so obviously outsourced.

[awemawson]

I played with the taper cutting program this morning, not working on the final part, and not even on the dummy I made yesterday, but the other end of the EN8 bar end that I had done a trial taper cut using the CNC mill.

This was just to try out feeds and speeds and check for vibration on the rather over long boring bar. As I feared it is excessive. I ramped up and down the feed rates and RPM but cannot get a 'sweet spot'


i fear that I will have to revert to more conventional tooling - I was trying the boring bar to give better visual access but it looks like it's a no no.

Despite the video giving the impression that the work is rotating in the wrong direction, it is in fact rotating clockwise looking at the chuck, cutting force being down onto the insert (tool behind the work).

[awemawson]

So I removed the long boring bar, but without resetting the machine over travel limits (due to the shorter chuck) I still had to use an axial tool with more stick out than desirable. However finish is dramatically improved so a basis for experiments and tests

[djc]

 Is there any opportunity to increase the stiffness of the tool by adding a gusset (or two)?

The one in the 'down' direction could be a 5mm plate with a triangle under it, bearing on some other part of the machine. Tool just sits on top of it.

The one in the 'back' direction might need a little more thinking about.

If you wanted to persevere with the boring bar, a big, hollow sleeve loctited to it with a square end bearing against the toolholder would help (eccentrically bored to put the extra material in the most useful place).

[awemawson]

Thanks for the suggestion - that sort of over hang is always going to give trouble I reckon.

If I'm desperate I can cut the tool shank to shorten it (but check first that the proposed length still reaches without entering the forbidden zone) but I don't want to really as that's a relatively new (and not cheap) tool.

[Pete W.]

What would happen to such a tool support if the program told the tool turret to rotate? 

[awemawson]

If all is well in the world, the PLC program should inhibit tool changes (and hence turret rotation) if the main lathe spindle is rotating.

If it DD happen due to a combination of several faulty circumstances it could be disastrous. particularly with the original chuck weighing over 47 kg and possibly spinning at 3500 rpm - that's a whole lot of energy stored 

[AdeV]

How big is that boring bar Andrew?

I've got a 32mm diameter one here which I've never used, and never will (it's far too big for my lathe), which I'd be happy to send to you... you can cut it down to the length you need..  The only thing is, it doesn't have through coolant.

[awemawson]

That is an extremely kind offer Ade, however mine is also 32 mm Ade by about 10" and would hurt if you dropped it on your foot 

The problem with that bar is the way it is mounted with so much 'stick out'. As it mounts perpendicular to the tool disk it's total length has to be exposed with only the depth of the holder contributing to rigidity. I could cut it much shorter but that seems a scandalous waste.

Using the conventional 25 mm square lathe tool with carbide inserts fully sticking out the finish is actually quite acceptable, however I have decided to cut it in half reducing stick out and have ordered a replacement to salve my conscience as it will be a usefully equipped tool holder for the future.

[awemawson]

After what seems a ridiculously long wait at last the postman brought me the new SDJCR2525M11 lathe tool holder. I didn't want to truncate the original until I had a replacement.

In practise I've been tied up with significant animal care issues this week as the other half has been away, so my life has been sheep, chicken and green house and polytunnel watering so probably couldn't have resumed work anyway until today. Mind you this HAS meant that the dogs and I can be in the best sitting room without risk of attack 

So - cut the blooming thing - well first careful measurement showed that I could only truncate it by 30 mm and still reach the work piece without the turret entering the protected zone, but 30 mm can be quite significant in terms of chatter.

Hacksaw job  Well just as well my hardness tester was to hand - measuring 415 Brinell it's a job for the angry grinder. Severed and tidied up on the disk sander it is now in the turret awaiting it's Z & X offset being measured. Hopefully I can do this tomorrow between guests checking out (two sets) and guests checking in (another two sets).

. . . only a little step forwards but at least it IS forwards !

[awemawson]

Argh . . . . this is becoming a nightmare 

I had overlooked the fact that the adaptor is only 45 mm thick off the mounting flange whereas the temporary 3 jaw manual chuck my test piece is mounted in is considerably thicker at about 140 mm to the relevant bit of the work piece meaning that far from shortening the tool I need to EXTEND it  76 mm 

This of course is why initially I'd used the fat boring bar but rejected it on vibration ground

 . . . . time for a rethink - I only need to turn about a 15 mm length of taper but it has to be 'dead nuts on' as far as concentricity and angle 

[hermetic]

You have saintly patience Andrew, I have been watching, but keeping quiet at the back of the class in case I broke your train of cogitation!

[awemawson]

It's getting sorely tried at times Phil ! This wasn't intended to be a saga to rival 'Noggin The Nog' !

I've taken up Ade on his very kind offer of a 32 mm boring bar that I can trim to length so hopefully I can pull something out of the bag.

I did actually investigate how to reset the 'Z Travel Software Limit', but it turns out that what is reported as exceeding the software limit is in fact a hardware travel limit set by cams and a microswitch. I could move them but I think extending Z travel by 75 mm past the designers intention is pushing it too far - I don't know what else such as ball nuts and covers and guides might suffer.

[Henning]

Not having worked on a CNC machine since the days you had to code everything on the machine I’m probably totally out of tune, but would it be possible to mock up something like a lathe steady rest for the tool? Would probably need some creative programming to ensure no crashes perhaps Anyways, quite enjoying the saga, and all the detours. Keep up the great work

[awemawson]

Nice idea Henning, but on a CNC lathe the bedways are not accessible to put things like steady rests on sadly. Hopefully a stubby boring bar will triumph.

Today I decided to tackle the setting up to drill those rather long oil galleries. The ports to join are on either face of the adaptor and need to be aligned precisely vertically. I reasoned that by inserting a 6 mm bar into each port I could somehow rotate the adaptor while mounted on an angle plate until they were aligned, then worry about lateral positioning.

(I need to drill 6 mm galleries through a land that is only 9.8 mm wide for practically the fully length of a long series drill)

It rapidly became obvious that having the adaptor held on the angle plate with a central bolt wasn't going to work. Adjustment in small increments was by rotation of the adaptor, BUT the centre of rotation kept changing as the bolt was a very loose fit.

What I needed was a close fitting pivot to rotate the adaptor on in a more controlled manner. (I'd considered a vertically mounted rotary table but one of the ports would have been obscured by the table).

Hunting through the scrap box, to my delight I found an old tractor hitch pin that was absolutely precisely the right diameter and it also was centrally drilled for a grease way which would aid drilling and tapping to put studs in the ends. Ah yes - BUT it's as hard as a witches titty. I did cut the bruised end off with an angle grinder but facing it on the lathe with carbide tooling was hard work and tapping it with HSS taps would court disaster. OK shove it in the forge and soften it ! Well common sense prevailed - it is full of grease in the central hole so it'll smoke the place out, and the fire will mar the currently acceptable finish.

Don't be a cheap skate I said to myself as I cut 100 mm off the end of my rapidly reducing stock of 50 mm round EN8. I turned it to a close fit for the bore of the adaptor (43.450 mm) and drilled and tapped both ends M12 having parted it of at 57 mm long to let it clamp in the 60 mm deep adaptor bore.

This pivot piece then bolted onto the face of the angle plate allowing smooth rotation with the centre of rotation staying put, unlike previously.

Next stage - do the adjustment, but I've been called away for the present.

[awemawson]

Now having the proper pivot, rotating the adaptor into alignment was far easier.

I had to modify the angle plate to allow the 6 mm bar into the lower hydraulic port, but that was just a quick trim with a carbide burr in the die grinder.

So having the two ports hopefully 'dead nuts' in alignment vertically, I picked up the edge of the flange with my 22 mm bearing edge finder, popped over (11 + 4.9) mm and set the X zero and was ready for drilling.

First up, a 6 mm end mill to start the hole as starting a drill on a curve would be impossible. Then when down about 20 mm, with copious amounts of lubrication and chip withdrawal I swapped over to a jobber length HSS Cobalt drill and gently took it to full depth. I continued to use the collet as it gave much more headroom than a chuck.

Then for the 'Long Series' as this is a deep hole. I only have HSS not HSS Cobalt - initially it went fine but then DISASTER my worse fears - the drill broke.

So I have 50 mm of 6 mm HSS drill broken off with it's tip about 60 mm from the surface - stuck firmly and not going anywhere 

Fortunately it looks that there is enough clear hole to give me an accurate start for an EDM electrode if I can find some 6 mm thin wall brass tube, and it's already mounted on the angle plate in the correct attitude.

 . . . .oh joy . . .

[awemawson]

Well I found some 5 mm copper electrode tube - there won't be much of a 6 mm drill when it swallows a 5 mm electrode!

Daren't leave it alone so it may be a late supper.

[awemawson]

I gave up last night, it was just taking toooo long. I had to remove the electrode tube as the machine has a habit of lowering it's head when the hydraulic pump isn't powered with the result that thin tubes get bent. This had the consequence today when I refitted it that it wasn't quite revolving true, but only a fraction. This messes up the servo feedback system as it keeps feeding and withdrawing as the electrode lightly brushes the wall of the existing hole. In the end I inhibited rotation, which I'd initially enabled due to the rather uneven broken drill end. But we were well past the drill at this stage and in virgin metal.

I'd decided to finish the hole with EDM rather than drilling, as the surface of an EDM'd part has been subjected to intense heat at a microscopic level, and with this alloy steel could well cause hardening that would break another drill.

When it finally broke through into the lower port I breathed a large sigh of relief, as not only was this particular disaster overcome, but the holes actually lined up 

Next job was to re-mount it on the milling machine, drill the upper port slightly deeper (5 mm) to intersect the long hole and then re-mount it to open up the top of the long galley to 6.8 mm and tap M8 to receive a grub screw to blank it off.

I went very gingerly and used an HSS Cobalt drill. Started the tap in the mill to guarantee verticallity and finished it by hand.

So after a lot of faffing about that is one of the two oil galleries created. I have ordered up HSS cobalt 6 mm long series drills for the next one, and also some 6 mm thin wall brass tube in case I have another disaster!

(I might tidy that rather ragged tapped hole up with an end mill)