Member postings for RobCox

On a surface grinder you might well have trued up the top of the mag chuck with the grinder itself (I did) so it's top surface mill will be co-planar with the plane of travel of the table.

You could achieve the same on the mill I guess, skimming the base of the vice where the workpiece beds to make it co-planar to the table travel, but I doubt many of us would want to "modify" (being polite) our milling vice like that.

Jason, I agree with your method, but I get the height of the contact below the top (x in your diagram) to be 0.0795/tan15 = 0.2968, which gives me a revised answer of 0.3326.

Thank goodness I haven't got to worry about maths exams any more!

My answer is clearly wrong, because half of 1.125 is not 0.625

Edited By RobCox on 16/12/2021 12:20:56

99.4 thou if my maths is correct.

If the slot width is 2W and the ball diameter = 2R and the angle of the slot sides to the vertical = A:

The ball contacts the sides a height of R.sinA below the ball centre.

The distance across the slot at the contact points is 2R.cosA, so the height below the top of the slot is

(W-R.cosA) / tanA, giving the height of the top of the ball above the top of the slot as

H = R + R.sinA - (W-R.cosA) / tanA

For R = 0.5, W = 0.625 and A = 90-75 = 15, that gives the answer above.

Shoot me down if I'm wrong.

Rob

I thought the reason for the angle block and the discs, which have flats milled on them is to ensure the flats on the discs are exactly parallel to the plane of the cut the mill takes. That way, when the blank is milled one side, flipped and milled again, the two milled sides of the parallel are exactly that, parallel.

If the base of the vice is not coplanar with the plane of the cut taken by the mill and one edge of the blank is seated against the base of the vice, whichever way you rotate it and recut it you will always cut a taper.

This might be a bit of a mad idea, but...

If you could get a transformer a bit bigger than the V block, take it apart so you have the E laminations and the windings left. Connect the thickest windings to a DC supply, put 2 limbs of the E laminations in contact with the V block and pass as large a current as the windings will stand from the supply. There should be a large magnetic field generated by the transformer coil which you are arranging to pass through the V block (with it in the ON position). This might reinforce the magnets strength (check which way round first, otherwise it'll try and demagnetise it or push the electromagnet away).

I'm guessing this is a bodge version of what would be done commercially.

helices

And if you want to do that you'll need the gear on the end of the mill leadscrew and the banjo and gears to get the desired lead on the helix. But... you can use the dividing head as it stands to index the gear blanks to cut them

Edited By RobCox on 17/06/2021 16:47:41

£33.40 + vat will get you a 4 piece puller set from simplybearings.co.uk. Usual disclaimer, just a satisfied customer. Buy for one job, end up using them many times subsequently and being thankful you had them.

If anyone wants a home brewed excel spreadsheet that will do the calculations for you (in imperial - but it could be modified to do metric as well, PM me an email address and I'll mail you a copy. I've used it many times as I don't have charts for 55deg threads and its served me well so far. I run it on my phone, so it's to hand when I need it.

Rob

Pete's thread:

**LINK**

My thread:

**LINK**

Rob

Yes I am😀. Try searching for RobCox instead!

The threads can be found on the Lathes and other machining equipment sub forum. Look for Eagle Surface Grinder Build. Enough information on what I did to cure insomnia!

Pete's thread is Eagle Mk3 surface grinder rebuild.

Rob

Hi Robert,

I may well be able to help you. I'm just south of Cambridge so not too far away.

If you PM me a phone number or email address, perhaps we can sort something out.

Rob

I think mine is some flavour of glass fibre reinforced material. I had to drill out a hole in mine to accomodate a new stop switch. I used an hss drill bit and it had nice smooth rounded cutting faces after drilling a mm or so.

Rob

I think the first video makes a right meal of things there.

I've turned brass on my woodturning lathe (I spent 25 years woodturning before getting a metal lathe). Treat the metal like a hard wood that you use a scraper on. The tool has a rounded profile viewed from the top. The front clearance is about 30 degrees. You need a toolrest that puts the cutting edge about centre height. The tool needs a handle and it should be raised above the axis of rotation. That way, if you get a catch/ dig in or whatever you want to call it, the cutting edge gets pulled down out of the cut. So no drama. The toolrest needs to be smooth to permit a smooth action to achieve the shape you want. Then nibble away gently at the workpiece to shape it as desired.

I've used this technique on steel to make a profiled handle for a machine without any problems. HSS woodturning scrapers are remarkably efficient at cutting metal as they are at wood. It comes down to practise and the skill of the operator to get a flowing curve on the workpiece.

Rob

CBN will grind both HSS and carbide OK.

I use a coarse grey wheel on one side of my bench grinder for rough shaping HSS before giving it a final polish on the CBN wheel. The CBN wheel is too slow for roughing, as it's a fine grain - I think. I originally got it for woodturning tools, but it's great for lathe toolbits.

Rob

Turn the hole to be smaller than the part it's to be mated with, at a ratio of about 1 thou per inch. Heat the female part with a gas torch (doesn't have to be red hot). Press together quickly! If the male part heats up before its fully driven home, game over!. The resulting fit is stronger that a press fit.

I don't see a problem with a gap bed. For hobby use you're probably not going to be pushing it hard enough for the gap to make a difference. From a rigidity perspective, I would have thought that the bed with or without the gap piece would be much more rigid than the tool fixing, toolholder fixing, topslide and probably the saddle gibs too.

Whether you'll ever need the gap is another question that only you can answer Maybe, like a lot of tools that I have, great for one job every few years.

Rob

As you have a rack, you should be able to determine the PA with a protractor. I'm in a similar position to yourself in that I have an Eagle surface grinder that I'm putting back together. In my case, the rack and gear are just worn, but there are enough good teeth on the end of the rack to determine it's MOD 2 with a 14 deg PA.

See the first link in Brian's post above. That's exactly the material the commercial offering would be made from.

When I renovated my elliott mill I junked the original handles as they were plastic and looking tatty. I replaced them with some nice cast iron ones from wdsltd.co.uk (usual disclaimer, no connection, just a satisfied customer).

They do a range of sizes, materials etc. Just one word of warning - the keyway will cost you! I bought mine without a hole as I needed to bore it to fit an imperial shaft and cut a keyway on the lathe (doubleboost style). As an example, a 100mm dia cast iron wheel is £11 + VAT without keyway, £25 + VAT with!

Rob