Member postings for Steve Withnell

I hope you are not suggesting one of those six jaw self centring chucks?

What are they for anyway?

One method of turning a crank in a self-centering chuck...

http://whittlev8.files.wordpress.com/2011/02/crank-cam.jpg

Steve

My call would be a 4 jaw self centering chuck - it will self centre round, square, oval bar and some weird forms (ie Stuart steam governor extrusion). I got one of these years ago and the only thing it can't help with is turning cranks. It is possible to use packing pieces to move the work off-centre, but I've no real experience of doing that.

A minor benefit is that the clamping forces are more even with four jaws rather than three (think about thin wall tube as an example).

There is no "right" answer this - get an independant jaw chuck and have to clock every job and be able to turn off-centre or take the benefit of the 90%+ times you won't need to clock a job but be stumped when you need to turn an eccentric.  I've never been convinced about self centring chuck runouts being a problem.

So it's really back to what you plan to do,  before you buy a second chuck.   In fact I just remembered how to turn cranks in a self centring chuck - l'll see if I can find a picture to upload...

Steve

Edited By Steve Withnell on 06/12/2014 16:31:38

Lot's of interesting theory and avoidance strategies here, but nothing to cover getting caught lifting an old ammunition box full of grubby magneto's out of the boot of the car...

Just working my way up...

Swapping solid nylon for solid PTFE should cause the CI to move from 50 to 70 ohms, but part of the reason the connector falls in bits when you turn the end off, is that the nylon is in part airspaced (and crudely so), so hopefully the difference isn't that marked...

To be honest I hadn't spotted that - so have been doing some back tracking

Steve

The one thing that really surprised me when I bought my mill as a new starter, was how just how massive the cutting forces are - my mill is an old Warco Minor, it weighs about 145Kg on the bench and yet the size of cut that can be usefully taken with a 12mm cutter is (from a novice perspective) very small indeed. The limiting factor is not motor power, but just lack of rigidity, even though a 145Kg lump of cast iron supporting the cutter is hardly trivial.

Here you go -

This is what the pocket was for - this is a butterworth response bandpass filter, the length of the copper rods is related to centre frequency (in this case 1090MHz ). Still a couple of holes left to drill and tap for the lid and each rod should have a brass 2BA screw to provide a little bit of tuning.

The BNC connectors are the typical "single hole" mounting type which happen to be threaded 3/8 x 32TPI UNEF. Plan was to turn the threaded part of the connector down so it was the same length as the wall thickness. Which worked except that the innards are effectively crimped in place so fall apart as you turn the crimp off. I've then used PTFE as a push fit to replace the original nylon dielectric. This eliminates the need for the crimp. PTFE is a) a far better dielectric at UHF and b) will standup to the heat from soldering the inner conductors to the copper bars. I'll be using soft solder and a small tip on my propane torch to make sure I've plenty of controllable heat. The copper bar should allow me to keep the torch well away from the joint..

Steve

Not so I'm afraid; electrochemistry dictates that the nominal voltage for a single lead-acid cell is about 2V, as are the single Cyclon cells.

Andrew

True! brain fade, my plugs are 2volt types!

Steve

The pocket turned out really well, hit all the dimensions and the 8.8mm tapping drill worked well, then managed to drill a simple straight through hole 1.5mm out - D'oh! Otherwise the whole thing is coming together really well. I'll tap the duff hole and plug it with a threaded Al rod and loctite, then try again.

So thanks for all the advice!    Must take more care over where I point that drill

Steve

Edited By Steve Withnell on 20/11/2014 21:40:36

I'm well on with the pocket, I bored the centre out, which worked well. I then moved the workpiece over to the mill and set the stops so I had about 0.5mm shy of each finished dimension. Then moving back and forward between the stops to get rid of the rest. Once I'de done half, I then tried chain drilling out the waste (with a slot drill), again working between the stops and this did seem to be more effective than milling it away, mainly less problem with chips and faster progress (remember I'd bored out the majority on the lathe already). I used a 10mm slot drill, but could only get 18.5mm deep, so I finished up the bottom of the pocket with a 12mm 3 flute end mill.

I then changed to a 5mm long series carbide "high helix" 3 flute end mill and have taken two of the sides (between the stops) to the finished dimensions. The finish has turned out really well. The last pass was 0.05mm at 20mm deep, climb milling with some tension on the table locks. Biggest cut was 1.25mm x 1.25mm - 25% the diameter of the cutter. I've got the mill running flat out at just over 2000rpm.

Shouldn't take too long now to finish up the remaining two sides.

After that there is just a load of holes to drill and a few to tap. Two of the holes will be 3/8 x 32 tpi UNEF - all the tapping charts I can find quote 8.85mm tapping drill, but don't quote any figures for thread engagement. How does 8.8mm sound in context of a through tapped hole in this casing? I need the male thread to "bite" into the casing to ensure a good electrical connection.

On the other comment - I've never had a cutter come loose from my collet chuck (ER32) in an MT3 arbor. BUT I've never done anything particularly heavy duty either.

Then there was O'Hanlon's law - " A PC full of memory will always cost £60". It's held good for 25 years...well roughly.

Sure it's 1.5volts and not 1.2volts for standard glo-plugs? The 1.2volts is derived from a single lead/acid cell. I think the "Cyclon" cells sold to heat glo-plugs are 1.2 volts. NiCads and other re-chargeables also produce about 1.2v.

Steve

Neil,

Once you've finished the adept, I'll send the courier round with my Dad's Brittania...it's got new lead screws on the cross slide and compound, so that's a start for you !

Steve

Thanks! Boring the core out of the material on the lathe is an interesting idea. Sounds like a good plan to leave the blank material oversize and clamp directly to the bed. I need to maintain a datum in X,Y, and Z for the pocket so will need to be careful the edges are "getatable" after clamping.

I found a 5mm high helix long series carbide cutter in the box so that sounds ideal for cleaning up the periphery to size.

The internal dimensions of the pocket are quite critical - it's not a box but an RF cavity. I've just tweaked the design a bit and the pocket turns out at 89.8mm x 68.8mm x 20mm. That means the walls will be just over 5mm rather than 2.5mm which will help considerably with the clamping problem.

Steve

Looks like the consensus is to chain drill out the pocket then tidy up!

Thanks

Steve

I have a piece of Aluminium 100mm long x 80mm wide by 25mm thick and I need to cut a substantial pocket in it using my round column Warco Minor (RF25/Chester Eagle variant) mill. It's happy with 12mm cutters, but much bigger gets to be an issue.

What is the most effective way of milling a pocket 95mm x 75mm x 20mm deep?

No corner must have a radius greater than 3mm and the tolerance on all dimensions must be better than +/- 0.1mm. The material is just off the shelf plate, nothing exotic.

It seems a simple task, but I haven't done this before and I suspect there is a best method.

Whats the expert view?

TIA

Steve

Fantastic stuff Neil, really impressed. I think I have a 1/8 HP 3 phase motor somewhere (with gearbox outputs 1rpm from memory) - if its interesting to you, I'll venture the depths of my hoard and take a look.

Steve

"Only the Paranoid Survive"... Andy Grove, CEO, Intel.

"Just because you're paranoid doesn't mean they are not out to get you"...Catch22

Steve

That deserves an award for "Outstanding Patience"!

Steve

Got fed up with my old netbook taking for ever to load Win7. Spent 30 minutes loading an unofficial version of Chromium OS and now I can post stupid remarks in under a minute from power on! Only bug to fix is the scaling on the mouse pointer...

Steve