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

[awemawson]

This morning I ran the two parts of the program that I split last night. But first I wrapped the 4th Axis in clingfilm to keep the machinable wax swarf out of it to save a bit of clean up time later.

First pass went very well, I was hovering with the workshop vacuum hoovering as the cut progressed as I don't want the wax in the machines coolant.

Second pass took ages to do not a lot until the very end. I'd had to specify a rectangular block of stock for it to cut. Although Featurecam allows for round stock I couldn't get the axis of the stock and the machining to be the same. In 3D view it looks perfect, but in plan they are misplaced - an oddity so hence rectangular stock and thus a lot of 'air cutting' before getting down to business. In the end the final cut was only about 0.5 mm and that (with all the air cutting) took 39 minutes !

I'm pleased with the results. I need to measure how accurately it's cut the 7 degree recess taper, I also need to replace the 22 mm 2 flute end mill for one with greater depth of cut - it manages but with very little margin - OK in the wax but probably pushing it in the final EN24T item.

[nrml]

That looks really nice. Almost too good to melt and recycle. Is is it a taper lock fit?

Edit:
I've just gone back a few pages to look at the drawing of the spindle and I see the taper there. Sorry for the pointless question.

[awemawson]

Thanks NRML, but . . .

No, the taper is a VERY relevant question as I have just realised that I mis-read the drawing, and what I understood to be a taper with limits of 7 degrees to 7 degree 30 seconds is ACTUALLY a taper of 7 degrees 7 minutes and 30 seconds (or 7.125 degrees).

I blame it on old eyes !

But this is what prototypes are for ! Imagine my chagrin if I'd gone straight to cutting that expensive EN24T billet !

I'm now wondering if  Male lathe spindle nose tapers and Female chuck tapers are actually manufactured to slightly different angles. The bolting face obviously draws up tight with the taper as a register but manufacturing to get the taper an exact snug fit when the flanges are tightly together would be easier if one taper was very marginally different. Amazingly hard to find dimensioned drawings of the chuck female 

My aim today was to turn up an accurate male gauge for when I make the real thing, but other things have got in the way.

[Muzzerboy]

That came out rather well. Good catch on the taper angle.

Do you plan to make some metal soft jaws? Presumably you will need something better than plywood for the real thing.

[awemawson]

Thanks.

I am hoping to turn the taper on the Beaver TC20 along with a reference bore up the middle that I can use to accurately centre it on the Beaver Partsmaster with the Hiedenhain probe as a second op. for drilling the holes and other features.  I can clamp it down for that operation. I only really milled the taper for a bit of fun to see how well it came out and the answer is surprisingly well, but you can feel ridges with your nail.

For boring the taper I  took delivery of a nice heavy 32 mm boring bar today with integral though coolant   

[awemawson]

I've been going crazy for two days trying to resolve an issue with being able to make this adaptor. The counterbored holes that the cap screws go in to mount it on the lathe spindle clash with the threaded holes that the collet chuck is retained by if both rings of holes are radially aligned '12'oclock to 12'oclock'. But in this orientation drilling holes to join the two sets of hydraulic oilways is dead easy.

If I rotate the A2-5 mounting arrangement to clear the A2-6 cap screws then there is no way to drill the joining oilway as one of the mounting holes is in the way.

But I had a flash of inspiration in the early hours this morning. The A2-5 collet chuck uses only 6 of the 12 possible mounting holes, and although the original chuck is mounted  by 6  M12 cap screws arranged in three pairs there is no need for me to use this pattern as the spindle nose of the lathe is drilled and tapped for all 12 positions at 30 degree intervals.

By much faffing about, rotating drawings and standing on my head I have (I think) at long last come up with a possible solution, that is each ring of mounting holes having 6 evenly distributed members but the A2-5 ring complete with driver peg hole is rotated 45 degrees counter clockwise relative to the A2-6 ring.

It's not ideal as the holes that I will have to drill and plug that join the oil ways in the A2-6 spindle nose to the ones in the A2-5 collet chuck mount are at an odd angle and rather long at 89 mm (6 mm diameter)

I now need to lie down in a dark room with a wet cloth on my head !

 

[nrml]

Perhaps doing those holes on your EDM would be more accurate than drilling them. Starting those holes at that angle on round stock and keeping them from wandering  for that length would be a challenge with a 6mm bit I would imagine.

[awemawson]

Well I'll certainly mill flats before centre drilling then peck drilling - even long series drills flutes aren't quite long enough, so swarf clearing is a must !

A few test drillings first I think !

[awemawson]

Having got totally confused with the relative location of the mounting and hydraulic holes on this adaptor I made up a 'prompt disk' with prints of the A2-6 on one side and the A2-5 on the other, and it rapidly resolved my dilemma. The problem was that I have drawings of the A2-6 spindle nose and  recess but only the recess for the A2-5 part, and on some it is not at all clear from which side they are viewed. This of course confuses the rotational positioning of the oil ways as the other holes are symmetrically placed.

Next issue was an oddity in Featurecam. You can define either a 'Boss' or a 'Pocket' from diameter and depth and you can give the side a 'draft angle' - I need this draft angle to be 7 degrees 7 minutes and 30 seconds - the program takes decimal fractions of degrees, so in this case 7.125 degrees which I duly inserted. Problem is, if you return to the pocket dimensions later for editing you find that it has truncated this to 7.1 degrees. The only place in the settings where you can set the precision of variables is set to XXX.XXX and changing it makes not a jot of difference 

However I discovered that there is a second way of defining the wall of a boss or pocket, that is by having a line on the drawing passing through X=0, Y=0 and at the desired angle to the Y axis, and this method SEEMS to give the desired precision, however the code it generates is MASSIVE ! Just the A2-5 boss on the adaptor generated 770 lines of code!

Anyway I wanted to test if indeed the precision was adequate before committing, and dug out a bar end of 102 mm EN8 round to use as a trial cut. All set up and program loaded to the controller it started off very well, until there was an almighty BANG, the expensive 22 mm cobalt roughing cutter shattered and the enormous power of the X axis drive carried on pressing the broken cutter mangling the work  It had cracked the CAT40 holder and mangled the BE180 collet
.
Stupidly I had accepted all the default values of speeds and feeds without checking them, and this was the result. Carefully looking at the damage to the stock I concluded that all the damage was above the finished surfaces, so if re-centred I could possibly continue if I could find another roughing cutter (it defaults to using a roughing tool followed by a finishing tool). Well I couldn't find one, so mounted up a 22 mm cobalt end mill, very conservatively changed the feed rates and started it off. The was 14:30 yesterday - it finished cutting at 20:30 last night - 6 hours of cutting - I don't think the Partsmaster has done such a long run EVER ! Got fed up watching it so rigged a camera to watch from the house!

The way it is forming the taper is to orbit the part adjusting radius and depth in minuscule nibbles to closely approximate the angled line that I defined as the draft, and of course this gets rather tedious!

The result is surprisingly good - surface finish not as good as a turned or ground finish obviously but it seems to fit OK. I tried measuring the resulting angle with my vernier protractor but to get anything like the angle is extremely difficult on such a short length. Bluing it the contact doesn't look too bad.

I must say though, this is not the way I will be producing the tapers on the final adaptor - I will rough the blank out leaving the A2-6 'pocket' and the A2-5 'boss' parallel sided, and turn them on the lathe hopefully getting a far better finish and fit - this was just a test but even when turning I need to define the angles so probably will have to use the swept line method anyway.

Still to decide how to fixture the part - the A2-6 mounting holes go all the way through so probably I'll mill that side first and use these holes before flipping the stock for the A2-5 machining.

[awemawson]

An exciting day today 

Firstly my son was able to deliver my haul of Soft Jaws won sight unseen on eBay all the way from Chippenham. Exciting for two reasons - due to Covid this is the first time we've been together for over a year, and secondly as there were far more in the box than I had thought - turns out that they are stacked two deep  Haven't had time to give them a proper inspection but I think a 'good haul'.

Secondly after he had left I was able to put the crane to it's intended use and remove the chuck to use it's female taper for making my male gauge in the next few days. It went largely uneventfully. Initially slackening the 6 massive retaining bolts, then when finger tight and the crane connected I applied a bit of lift and fully loosened the bolts. Initially there was an ominous creaking, and I realised that I hadn't withdrawn the spindle reducing sleeve that stops bars whipping in the tube. Quickly knocking it out with a bar through the chuck all was well, the chuck came away nicely, and although blooming heavy to manoeuvre it was successfully pivoted to clear the lathe enclosure and lowered onto my pump up trolley.

No excuse now not to make that taper gauge !

[awemawson]

I managed to get my hands on a very nice Pratt Burnerd Super Precision MANUAL 200 mm chuck (9210-02005) with a plain back end and face mounting, so I thought if I could get a suitable A2-6 chuck adaptor plate of the 'semi-finished' variety I could turn the required 160 mm register on it and mount it up for those quick and easy one off jobs. I would need to incorporate some way of blanking off the hydraulic open & close lines that emerge at the spindle nose otherwise not only would oil go everywhere, but the PLC wouldn't allow the spindle to turn with no clamping pressure registered.

In the event the backplate supplier hadn't got the semi finished backplate but he DID have a fully finished one all ready to go. OK I parted with one of my few remaining limbs and ordered it.

When it turned up it fitted the chuck beautifully, a lovely bit of Polish (Bison) machining, but the spindle end, although it had the correct A2-6 taper and bolt holes, it wouldn't actually engage far enough to fit. The original hydraulic chuck had a boss projecting about 9 mm whereas the adaptor boss was only 1.2 mm - argh !

Speaking to Ian at Rotorgrip  who supplied the back plate and exchanging pictures it dawned on him that there was a extra shroud surrounding the spindle - removing that all was sweetness and light and it fitted like a glove. I think the shroud, which is a very heavy chunk of turned stainless steel, was probably to eliminate a swarf trap caused by the long original boss.

But I still had to stop that hydraulic oil somehow. Investigating the plumbing soon showed me that the two flexible hoses for open and close were routed to the rear of the spindle and fixed by easily removed conical fittings. As it happens I already had the proper male and female 'stop ends' for this range of fittings left over from my long gone JCB 3CX, so blanking them off and tying them up out of the way was easy.

OK chuck fitted, tightened down and a few tentative spin ups and downs performed to check it didn't fly off, then a spin test at 2000 rpm and nothing flew off - phew.

This chuck will be handy making the collet chuck adaptor, but I need to make a chuck key with a sliding bar as a standard one is fouled by the lathe tin work.

[rklopp]

Did you have a part in the chuck when you spun it up? Do not spin up a scroll chuck with nothing chucked unless you want yourself or a bystander to eat a jaw sandwich. The scroll’s inertia can activate the jaws on heavy acceleration or braking. I’ve seen it happen.


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[awemawson]

Also the clamping force decreases markedly as the RPM increases. I've a Pratt Burnerd clamping force meter that measures the squash and I/R transmits it to a second part. I was amazed how great the effect is due to centrifugal outward forces on the jaws.

[awemawson]

So having acquired all those soft jaws I landed myself with a bit of a storage problem as they were very much in the way in their crate and pretty immovable. I've been trying to find ex factory stores drawer units on the second hand market but it seems that they've gone trendy with prices through the roof. So as something had to be done I bought a pair of brand new five drawer roller cabinets on eBay. Despite being advertised as coming from London they come from Germany 

Anyway they came, I assembled them and have got the jaws at least vaguely sorted and they are now at least moveable as the cabinets are on castors.

So now I can get back to sorting out that chuck adaptor !

Have some boring pictures of drawers !

[awemawson]

Last night I had a flash of inspiration. If I made an 'insert' in the centre of the adaptor that had the drilling for the hydraulic passageways, not only would it be far easier to make eliminating very long and slender drilled holes, it would mean if I cocked it up I'd only lost a relatively small chunk of steel not the major chunk. It could still seal by squashing O rings against the chuck face and the spindle nose, and could be located by a pin or a set screw.

Drawing it up this morning I found to my chagrin that if it was a large enough diameter to encompass the O ring locations, then it clashed with the locator hole on the nose so very sadly was a none starter.

Then I thought, OK, eliminate the long drilled holes by milling a deep groove between the ports that need joining, mill another groove around the first to take an O ring laid in in an oval pattern and again sealed by squashing against the spindle nose. I've been kicking that around all afternoon on Autocad, and try as I might cannot generate sufficient clearance using the current hydraulic port size of 6 mm and the current O ring thickness of 2.5 mm cord. I can possibly marginally reduce the port size, it will slow down chuck operation but would work, and I could possibly reduce the O ring cord size and stll get a seal - it's working at about 500 PSI so not enormous by hydraulic standards. I need to go away from it and cogitate as my head is spinning! 

[awemawson]

And here is an illustration of the Groove approach and it's associated oops ! The two hole patterns are here rotated 15 degrees relative to each other to give maximum clearance. Trying other rotations results in problems elsewhere.

. . . .my head hurts 1

[WeldingRod]

I hate to suggest 1mm cord...

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[awemawson]

Yes I agree, but A:/ I'm not sure how well it will pressure seal, and B:/ I don't fancy cutting those oval grooves with a 1 mm ball ended mill in EN24T, but then I'm just a coward 

Experimentation called for I think

[WeldingRod]

They seal just fine.  We use them at 10,000 psi and up.  Kind of easy to nip/ damage/screw up... You should buy the harder durometer, though.  As a face seal you wont have any issues and it will give you more margin on extrusion.  You don't get a lot of squeeze on them.

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[WeldingRod]

Oh, I forgot: square groove corners are fine.  It's not worth messing with a ball end mill.

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[awemawson]

OK I'm getting fed up playing with possible O ring shapes and locations, time to have an overview think.

The original idea was to drill a very long thin hole from the outside of the adaptor, and bung it's open end with a sealed grub screw thus joining the two oil ports. I'd rejected this not liking the idea of drilling that long hole with a drill that would potentially wander all over the place.

Why not do a test ?

The feature on the adaptor that needs this 6 mm diameter hole approximately 110 mm deep is only 11.7 mm wide so not a lot of wiggle room hence my concerns. I happened to have an 'unknown specification' bit of 12 mm plate, so I shaped it to the same radius as the periphery of the adaptor so as to be a true test of starting a hole on a curve, then drilled two 6 mm holes where the two oil ports are that need joining. I don't know what the plate is, but it spoilt my new M42 bandsaw blade and I reverted to the angle grinder.

Setting it up carefully with the two holes perpendicular to a set square in the vice of the Bridgeport, I then found the centre of the plate in the Y direction using my 'ball bearing edge finder'. Setting the DRO to a Y=0 datum I then chucked up a piece of ground 6 mm bar just touching the front edge of the plate, and used it by eye to find the X location of the two previously drilled 'dummy oil ports'

Then loading a 10 mm slot drill in a collet I milled a flat on the curve of the plate as a starting point, which I then centre drilled. Moment of truth now. Chucking a standard length 6 mm drill, and with much oil and pecking for swarf clearance I took it to full depth. This was still not in danger of penetrating the oil ports. Now the REAL moment of truth, in goes the long series 6 mm drill, and this is going to have to break through into both those holes. Drills tend to grab when they break though, and I know from previous use that these particular drills are quite fragile so gently does it Andrew !

First hole reached and broken through without drama, however going deeper on towards the next oil port swarf was being pushed sideways out of the previous oil port and making alarming noises and grabbing. (The long series drill, and the depth of the plate meant that I couldn't quite totally withdraw the drill for swarf clearance without removing the drill from the chuck, which I did a few times)

OK eventually the drill passed through the second oil port and I went a few mm further just to give a good edge to the hole.

Breaking down the set up and inspecting what I've done actually showed that the drill has NOT wandered significantly and probably this will be the method that I use in the final adaptor.

(Here I was just risking breaking a relatively cheap drill and a bit of scrap plate - it will be a different matter with the actual adaptor!)

[modeng200023]

 

[tom osselton]

Well done I just watched a video on deep hole drilling last night.

[RussellT]

Hi Andrew

Do you think a close fitting plug in the holes would reduce the risk of breaking the drill?

Russell

[awemawson]

That's a good idea Russell so long as I can stop it rotating when the drill touches it, and also recover the bits after drilling.