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

[awemawson]

I made it a few years back after Ade made mammoth chunks for his dry sump machining - thread here I think:

https://www.madmodder.net/index.php/topic,7213.msg77229.html#msg77229

I got hold of a sack of plastic injecting pellets they were MDPE and  I bought candle wax pellets in large quantities on eBay. IIRC it was about a 50:50 mix and gentle warming, wax first then stir in the MDPE.

Some people use actual candles and plastic bags.

[AdeV]

Some people use actual candles and plastic bags.

Been there, done that....

I used some plastic pellets I bought from a supplier (they were LDPE rather than medium density), and some scrap candle wax I bought off eBay to make mine. Ratio is 4:1 wax to plastic, although there's plenty of scope for variation. I think the late John Stevenson compared a sample of mine with some commercial stuff, mine was a bit softer, but not a lot in it.

[awemawson]

I've used plastic milk bottles, cut up blue water main, and eventually some injection moulding chips from the Polypipe factory used to make underground water fittings.

Thinking about it I seem to remember that I got my wax pellets from you Ade 

It all machines nicely but sharp edges can be fragile.

[Muzzerboy]

Sounds as if polythene / LDPE actually dissolves in paraffin wax if you heat it. Is that the case? The thermometer in that other thread suggested 170C. You live and you learn!

[awemawson]

Yes, heat the wax up to melt it and slowly stir in your chosen plastic.

You have to be careful not to set the wax on fire by heating too fast !

[awemawson]

A bit of progress:

I've inserted PTFE shims in the crane pivots and done the bolts up with lock nuts - previously if tight enough to reduce play, pivoting would undo the nuts making it slack again. Now the pivots can be tightened quite tightly and yet the arms still pivot with minimal play.

Crane now removed from the machine to allow me to install jaws to hold the 170 mm billet of EN24T. In my box of used jaws I found a set that are already very close to size - in an ideal world I'd prefer a bit more jaw thickness on the outside of the billet but the only other ones I had would need masses of material removing precluding their use in the future for small (more usual sized) things. I console myself with the thought that the cutting forces will mainly be towards the chuck in the Z direction pressing the billet into place. I've yet to finish bore them for concentricity but they are very close.

To fit these jaws, previously used by someone else on a different lathe, I had to modify the Tee nuts as they were 'bottoming out' before gripping - not good in use !

This meant steaming up the Beaver Partsmaster for the first time in ages, and darn me the Kurt vice had decided to seize solid so that took a bit  of freeing of. Anyway the upright of the Tees was duly reduced by 5 mm and on went the jaws.

. . . but that's enough for today.

[Muzzerboy]

I made a swinging arm to hold the entire control cabinet and display unit for my Bridgeport CNC conversion, using a length of 2" square tube. The swing pivot used a couple of Chinesium ball bearings from a set of 10 that I bought for the spindle motor (the one you now have in fact). The main downside is that it swings out of the way if you so much as push it with your finger, so it also requires a stay to hold it at the right position. They are another option worth bearing in mind for this sort of application if you get sick of messing with soggy PTFE bushes etc.

[jiihoo]

Nice!

I was staring and then zooming at the picture of the two 26 TPI thread gauge blades and I am quite certain that the first one reads "25". A somewhat smudged "5" but a 5 nonetheless. The upper left of the number looks like it has a sharp corner and it looks like there might be a break below the horizontal bar on middle left.

[awemawson]

Jari, looking at it again closely under a magnifying glass I think that you are entirely correct 

[jiihoo]

Glad to restore your faith in Moore and Wright 

[awemawson]

So a bit more progress. The other day having increased the depth of the soft jaw retaining bolt counter bores I was able to fit them and skim them to a close fit for the billet. I still feel that they are rather skimpy, lacking thickness outwards, so it'll be light cuts only. To use a new set of jaws and bore them is obviously the best option but taking them out far enough to hold 170 mm vastly reduces the chance of them being able to be used for other things, and at £60 per set to replace,I don't want to waste the ones that I have.

I've still to form an undercut in the corner of the jaws, but as this again considerably weakens them I may bevel the billet on the manual lathe so that it can sit snugly without the undercut.

I've made some progress on the CAD side, downloading a DXF of a Kitigawa A2-6 chuck and importing it into FeatureCAM and deleting all but the A2-6 back end. I've got a working model, but need yet to match the tool crib on FeatureCAM to what I have on the lathe.

I'll put pictures of this up later when it's progressed a bit more .

[awemawson]

Now today's task was to produce a suitable 'test  billet' of machinable wax to save trashing the extremely expensive EN24T final one.

The pre-cast slabs of M/W that I already had are a bit too thin but I decided to cut one anyway on the band saw, but also cast one to size thereby using up the bits from bandsawing the slab.

I am slightly concerned that the clamping force of the lathe chuck will be too much for the machinable wax, and this thinner billet can be used for tests. The lathe has two pre-set clamping levels - high and low - I need to investigate if I can reduce the pressure of the low setting even further. (Selection between the two levels  is by M codes)

So taking my life in my hands I raided the kitchen and found a nice 7" cake tin with a 'drop bottom' Ideal at 177.8 mm diameter as it is just over the 170 mm of the steel billet and the M/W shrinks considerably on cooling.

Then I went hunting for the pot that I had previously melted the M/W in - turns out that it was a Kennedy 'Red Hot Dip' pot for their version of Crocell tool dip. Evidence of previous use was obvious - there was still some M/W in the bottom!

So, pot set to melt - it's thermostatically controlled and I took the M/W up to 150 C very slowly giving frequent gentle stirs to get in homogeneous.  I wanted to pour it at the lowest possible temperature to avoid major shrinkage.

Now it is poured I'll leave it over night to cool and shrink-release from the cake tin. I do hope it comes away cleanly or I'll be in trouble 

[awemawson]

Inspecting the 'cake tin billet' which has now cooled to 50 Centigrade it has already shrunk considerably.

But I'm in the workshop to investigate high / low setting of chuck clamping on the TC 20s not cooling wax!

M81 selects 'high clamping force', M82 selects 'low clamping force' and the hydraulic pressure meter in the headstock end cupboard displays the selected pressure, and this cupboard also houses the pressure setting and selecting valves. Easy really - twiddle the pressure knob and watch the gauge!

So putting in the band sawn billet and selecting low pressure it crushed the billet 

So I reset the low pressure to 'very low' (see picture) and still the chuck took another bite out of the billet - argh !

It looks like I'm going to have to think again about what to use for my trial cuts 

So I video'd the PC screen as FeatureCAM was chewing out a demonstration A2-6 'chuck back end' as a consolation prize:

[tom osselton]

Can you place something between the jaw and wax to get more surface area on the edge?

[awemawson]

I was wondering on similar lines, but I think it will be marginal whatever I do with the m/w. I may end up casting aluminum ‘prototype disks’ but there’s quite a volume of metal there.

[Sea.dog]

Are you machining just the outer face, Andrew? If so, why not mount it onto a piece of 18 or 25mm ply? From the simulation there is a lot of meat left where you could sink in screws with large washers.

[awemawson]

The final version needs both faces machining, so the holding arrangement needs to accommodate accurate reversal.

Was going to cast an aluminum blank today, but got distracted by discovering a rather serious data loss - when I updated computers several months back I seem to have lost all the post processors and tool cribs set up on FeatureCAM for the Beaver Lathe, Beaver Mill, and the Fanuc Tapecut Wire eroder. Quite a lot of work needed to re-create them. It seems somehow they didn't feature on the backup list but I thought I'd done a complete back up of everything including the kitchen sink 

So this afternoon I need to create another Win7 machine and hope the HDD that I put in my safe has the data on it 

[Sea.dog]

Ouch! 

[MetalMagus]

Create a post with a base, like a candle stick, that you can hold in the chuck and mold the wax / plastic around it. That way you can clamp properly and machine diameter and face. Might to be more like a mug tree with arms radiating from the centre spindle to give the plastic something to react against to resist slipping when turning it.

Sean

[awemawson]

Sean, I think I'll go with an aluminium blank - time I actually cast something useful now the Induction Furnace is back up and running . . .

. . . . BUT  I've spent a couple of very frustrating days tracking down back ups on various old PC's and stashed hard drives, but NONE of them have the post processors for the Partsmaster TNC355 CNC mill or the Beaver TC20 S Siemens 820T CNC lathe. The only good news is that I think I've recovered the post processor for the Fanuc Tape Cut Model L  wire eroder with it's Fanuc 6 controller (but yet to test it)

What I HAVE learnt - which is very handy - is that the Windows Backup and Restore saves it's backup as a "VHD" file which Disk Management can 'Attach' as a virtual hard disk, so that you can view and access individual files without having to restore the backup onto a machine in it's entirety .

[awemawson]

OK Wire EDM post processor fully tested - I found a FeatureCAM  drawing of an involute gear that I had cut some years ago, and also the associated G-Code file. Ran the part through FeatureCAM with the newly re-found P-P and produced identical G code - so - Phew that's one definitely sorted 

I also found an X-Build (the program that allows P-P generation) ".CNX" documentation file for the modified Siemens 810 P-P that I'd been using on the 820 on the lathe. Now the .CNX file is a form of the P-P that can be printed out and read, whereas the .CNC version is the one FeatureCAM wants. Given a .CNC file X-build can spit out a .CNX file but I can find no way of reading back in the CNX file to X-Build. OK the information IS all there and I can manually type it in but there's 10 pages of A4 . Some of it can be 'cut and pasted' but the majority is 'drop down boxes' or 'tick boxes' that need filling in.

The PP for the TNC355 in the Beaver Partsmaster CNC Mill was I'm almost certain actually a standard one for a Heidenhain TNC155 with a tool changer - I don't remember modifying it much if at all.

Had enough of it today, hopefully I'll knuckle down to it tomorrow.

(.CNX file attached but renamed .TXT to allow upload)

[awemawson]

Having spent some while recovering the Post Processor and Tool Crib for the Beaver Partsmaster in Featurecam following my data loss I decided that a good test would be to mill a prototype of the A2-6 to A2-5 chuck adaptor in machinable wax.

To this end I manually turned the blank that I cast the other day and crushed with the hydraulic chuck to a 'tidy finish'. It's now ready to mount on the Beaver Partsmaster CNC Mill somehow. And that somehow is the next issue 

It turns out that my Kurt vice on the Partsmaster easily opens wide enough to take the blank but I will have to make some semi-circular wooden jaw pieces to spread the load or it will be crumbling again.

But that's a job for tomorrow

[awemawson]

So today I went through the tool crib on the Beaver Partsmaster making sure that it matched that that I'd put into Featurecam - it almost did and now it does !

Then I re-set all the tool offsets using the Heidenhain probe, and mounted up the machinable wax 'pill' in the Kurt vice with a pair of semi-circular wooden 'vice jaws' that I'd made on the bandsaw to spread the crushing load.

Getting close to cutting 

Again using the Heidenhain probe I found the dead centre of the wax pill and set is as X=0 Y=0 but set Z zero as about 50 mm ABOVE the surface to do a trial run to see if thing looked sensible.

Time to load the program. Well firstly I found that I'd lost all the coms settings for TNCServer which is the program sitting on the PC that makes files available to the TNC355 in the Partsmaster, so a bit of flapping around recreating them. Now to remember how to do it - a few false starts surrounding TNC355 file naming conventions and code line numbering and we are off - program down loading into the controller.

 .. ah . hang on . program is too large to fit in memory, it needs to 'drip feed' so I set it going and we have (sensible !!!) motion from the machine hovering it's tools above the actual work level until . . . ILLEGAL PROGRAM CODE pops up on the controller screen around line 250 . . hmm ? OK then it dawns on me - it's calling a 'label' to reuse code like a subroutine, but when drip feeding the code isn't all retained in memory - you CAN'T call labels !

Program limit is 1000 line in the TNC355 - my program is 1004 long 

Now I'm sure that I can do a bit of pruning - for instance cutting wax I don't want the coolant on so there's a few line to cut, but in the final run on steel coolant definitely WILL be needed.

So I'll probably split the program into two bits - but that's enough excitement for today !

(I do find using the fragile probe with it's ceramic tube probiscus rather stressy !)

 

[awemawson]

This evening I've split the program in two by only including certain 'features' in the Featurecam source and managed to load them both into the controller at the same time. Together they obviously total more than the 1000 line limit, but individually they are less (861 and 146 line respectively, 1007 total). Obviously with two files there is extra 'topping and tailing hence the extra 3 lines)

So very odd 'file storage' in the TNC355 - they have comparmented it into program boxes of 1000 lines each with no dynamic re-allocation of space - strange

[tom osselton]

I haven’t got my machine going yet I have sent the MMC card off to Cincinnati to be reflashed and a new battery and have purchased the Titan Dnc in anticipation of the larger file sizes.