Servo Driven 4th Axis for CNC Mill

[Pete.]

Bacon? Yup, yup, yup

&t=4m55s



     

[awemawson]

Well today went pear shaped from the start !

Cut a long story short, but because of some early arrivals that weren't expected until the end of the month, no time for clamp making so I bought these

[awemawson]

So what were the early arrivals? Two Ewe lambs and one Ram Lamb

[awemawson]

So the 'Lambing Tent' that was scheduled to be put up during the coming weekend had to be put up today in a hurry. This is an ex Chinese Army inflatable Field Hospital that is stored in two pallet mounted boxes, and needs a road compressor to put it up.

We got it up  after a few setbacks and the sheep are at least now safe from the foxes.

[NormanV]

Cor, you molly-coddle your sheep. On the Falklands, where I lived for a few years, the sheep only come inside for shearing and slaughter!

[awemawson]

I seem to remember that there are no foxes on the Falkland Islands. We'd loose too many lambs to the little b****rs otherwise.

[NormanV]

 You're absolutely right, and there are vultures to get rid of any stillborn ones!

[John Stevenson]

Flash bastard, anyone else makes do with a taup draped over a tractor.

I'd be a bit careful putting that up where you live.
You are very close to the tunnel and next thing you will have 567 Romanian families kipping in there and nicking everything not welded down.

[Sid_Vicious]

 

Flash bastard, anyone else makes do with a taup draped over a tractor.

I'd be a bit careful putting that up where you live.
You are very close to the tunnel and next thing you will have 567 Romanian families kipping in there and nicking everything not welded down.

Isn't that just another type of new arrivals?

[awemawson]

The clamps I ordered arrived today and I managed to find five minutes to fit them

[awemawson]

They work and certainly hold the 4th axis securely, but in the long run I'll probably make up a custom clamp as these are a bit chunky as a semi-permanent fitting.

To celebrate I mounted a bit of 1" bar and mandraulically milled a square and a triangle, really just using the 4th axis as an indexer. Although the brake is fitted and worked well, I've not yet run compressed air to a convenient point, so this was done with no braking. No sign of chatter what so ever so for many things I probably don't need the brake - but I will run the air anyway.

[Pete.]

That's wicked Andrew.

I have a idea for some mirror mounts for my bike that would require 4-axis milling. Any chance you could do a small job for me when you have the air piped in?

[awemawson]

Do you have a sketch or drawing ?

[Pete.]

No, but I will have soon!

The problem is I do a lot of filtering through city traffic so I probably fold my mirrors in a dozen times a day or more. This causes them to be loose, and self-folding above about 50mph. I have an idea to cure it but no idea how to machine it manually.

I'll do a sketchup or something.

[awemawson]

So the next task is to sort out a tailstock for use with the 4th axis.

I picked up this one, which is bored 2 MT and really intended for a dividing head, as it's a tilt and height adjustable one:

[awemawson]

The 80 mm diameter plastic hand wheel was smashed, and it was a bit of a mystery how it was fixed, until I turned the remains off carefully on the lathe. This revealed that it was an 11 mm shaft with loctite and a taper pin. Ebay kindly provided me with an identically shaped handle (but black not grey!) however the mounting was an M10 thread. So the 11 mm shaft got turned down and threaded thus:

[awemawson]

I will need to bore a hole aligned with the axis of the barrel to allow knock out of the morse taper using a tapping rod, as there is no other provision. I strongly suspect this is how & why the original handle was broken.

This mornings job was to make a stepped key for the base. The milling machine has 18 mm Tee slots and the base of the tailstock is grooved 16 mm, so a bit of milling this morning produced this:

[awemawson]

I am a little concerned that automatic tool changes may take tools ever so close to the tailstock, so at the moment I'm seriously considering making a cardboard mock up of the size of the tail stock and performing a few tool changes to prove that there is clearance. It's remarkably difficult to see during a tool change cycle exactly where in space things are as there's no real reference point for the eye to latch onto !

[Pete W.]

Hi there, Andrew,

I am a little concerned that automatic tool changes may take tools ever so close to the tailstock, so at the moment I'm seriously considering making a cardboard mock up of the size of the tail stock and performing a few tool changes to prove that there is clearance. It's remarkably difficult to see during a tool change cycle exactly where in space things are as there's no real reference point for the eye to latch onto !

Maybe Wax would be better then Cardboard? 

[awemawson]

No Pete I want something that will just be swept away without damage - it's my Heidenhain probe I'm most concerned about. It's pretty well the longest tool in the crib, and definitely the most delicate as the ruby is mounted on a thin ceramic tube that would easily break if it hit wax. Whereas a thin card mock up would probably not damage it before I leap for the ESTOP button.

I may be able to find a parameter in the control that slows the motion down during tool changes, and thus be able to avoid the Blue Peter modelling approach

[awemawson]

.....ah...... a solution has presented itself 

It turns out that although the feed rate over ride control on the panel will not allow traverse speed to be increased during tool changes, it will allow it to be decreased 

I knew that the over ride control was over ridden during tool changes but I thought that it was both for increase and decrease. But no, I can slow it to a crawl and watch and measure as in the fully slowed position it can be stopped - result !

[Pete W.]

Hi there, Andrew,

Fair enough and I'm glad you have a way forward.

    

I thought I'd set up my profile to display the time at my longitude but I'm posting this at 16:20 GMT and your message says it was posted at 16:47.         

What am I doing wrong?          

[awemawson]

As far as I know I've never set anything up for longtitude on the forum other than put the country as UK. I've just had a poke around my profile and found a setting to have an offset from 'forum time' with an auto-detect feature that says it is to display local time. Clicking this gave a four hour offset so maybe this post will bear UK time.

Later edit - Nope shows 4 am ish !!!!! unless the 24 hour clock is wrongly implemented and it means 16:00, but it shows as 04:.. which is early hours in the dark  even though it SAYS PM !

[awemawson]

The new knob for the tailstock arrived today, and promptly had an extra hole drilled in it to allow the use of a knockout bar to remove the No 2 Morse centre.

Whatever the plastic they made the handle from is filled with it's abrasive stuff - took the edge off an end mill in no time short !

[awemawson]

Now the eagle eyed amongst you will notice that the clamping bolts have their nuts on the 'wrong side' for placing the tailstock on the left hand end of a milling table as I must. The pair of bolts used to clamp it at a particular elevation and tilt, once set, should not need adjustment, however the clamp for the barrel will need to be 'got at' every time it is used. It would be easy just to remove the centre section and assemble it the 'other way round' but it would be nice to have ALL the locking bolts on the same side.

Then I suddenly realised that all that stops me putting the bolts in the other way round is a small groove milled to take an anti-rotation peg that is part of the bolt head