Member postings for Bubble

Hello all

Anyone studied the latest MEW cover picture?

Jim

Hi all

A man a plan a canal Panama

an engineering palindrome

Jim

Hello

In my day on the Railway they referred to drawing board sizes

Jim

Does anyone know the correct amount that a myford tailstock should be higher by? Im'e thinking of myfords original spec tolerances.

regards

Stephen

Myford (Beeston that is) used to selectively choose the base plate thickness on the tailstock on assembly of the machine, to give the proper alignment of centre height. The design error was zero plus minus.

Jim

Hello Windy

Not sure what your shaft is being pressed into.

However, on the full-sized railway, when pressing axles into wheels, the axle pressing-in force varied with the way that the wheel was supported. If the wheel was supported at the hub, close-in to the axle, the force required was correct to design. However, if the wheel was supported at its rim, the force required was too high. This was because "dishing" of the wheel under the pressing in force caused it to nip onto the axle. I experienced this on (as I recall) a Eurostar wheelset (under lab test, not production) and asked an old hand what was going on.

Jim

Hello John

Velocette clutch springs are 4.5 id, 1.1 wire diameter, 30 long

can be shortened and will give your solid length as 8 turns are 20 mm free length

Obtainable from Grove Classic Motorcycles (no connection) at 50p each plus postage

Their reference is C12/4 (Venom,Viper, Mac etc)

Jim

Hello Geoff

As the rotation of the shaft is only a few degrees, how about using bonded rubber bushes, the sort that have outer and inner steel sleeves bonded to the rubber. These can be flexible in torsion but radially stiff. Just an idea.

Jim

Posted by Bubble on 18/08/2015 16:14:29:

Hello Mark P

...

Of course, eye protection, gloves etc.

Jim Tut, Tut, never use gloves on lathes, drills, rotating machinery,

Hello all

"Never" And there's me thinking that people on here use common sense.

Here's a link to a sensible man **LINK**

Jim

Please note that I am completely out of my depth here.

Whilst searching for pictures of the Loughborough drop-test rig that I mentioned earlier: I happened across this report on a previous Hunter accident. ... Those with the appropriate technical background may find it of interest.

MichaelG.

Hello MichaelG

Did you pick up in that accident report that this was the Hunter that was in the Aero & Auto department at Loughborough in the early 60's

I sat in it often, dreaming!

I remember that one Saturday (yes we had lectures on a Saturday then) the airframes instructor Jim Oates was away so we decided to do him a favour and top up the tyre pressures on the Hunter. It took us about 2 hours to remove a wheel (they were big!) and roll it down to the shop compressor at the Auto end of the department, only to discover that the compressor only produced about 100 psi and the tyre already had 150 psi in it. We then had to work "overtime" to reassemble the landing gear.

Jim

Edited By Bubble on 29/08/2015 13:54:59

Hello Mark P

For reasonably short lengths of wire around a metre:

grip the wire at one end in the lathe chuck

Take a piece of hardwood say 300 long, 30 x 20 mm, with a hole in the middle a reasonable fit to the wire diameter

poke the wire through the hole, move the wood up close to the chuck, hold the hardwood at an angle to the wire, say 20 degrees

run the lathe at slow speed

slide the wood along the wire towards the tailstock

What you are doing is to yield the wire while it is rotating

Of course, eye protection, gloves etc.

Jim

Hello All

Has anyone on the forum tried case hardening using Granular Activated Charcoal (GAC) pellets?

I have a borehole water system here in Wales which uses filters containing this. I have not had the opportunity yet to try using the material from a "spent" filter. (I also have a big tin of Kasenite so there has not been the necessity to experiment, as this will last me another 50 years and I'm already 70!)

Used filters would probably be available for free from domestic water system engineers (there's lots of borehole systems in Wales) and as far as I know they are not recycled in any organised sense.

Alternatively, GAC can be bought on the web at about £10 per kilo.

Jim

Hello Stuart

Some years ago on my Hobbymat mill circa 1980 vintage, I bored out the original MT1 to MT2. I used the Chaddock method (in his Quorn book) to support the spindle in its own bearings in the lathe steady. As far as I remember I used an HSS boring bar as the spindle was not too hard. I can't remember if I set up the topslide or used my taper-turning slide (as designed by Chris Heapy). The conversion was (and still is) very successful. The Hobbymat head is now mated to my Tom Senior mill.

The spindle design is very good and why they were made with only a MT1 bore puzzles me.

Jim

Hi all

All common steels have essentially the same stiffness, just different yield points.

Jim

Hello Hopper

In BR Research we used to carry out high-temperature fatigue testing (among a few other activities), using extensometers that worked up to about 1000 deg C. We used to make fittings for these using a natural machineable material called pyrophyllyte. This was machined using ordinary HSS tools, by then fired in the test furnace and became a hard ceramic. There is also a machineable ceramic called Macor. Google has results for these. It is available down to quite small blanks eg 1/4 inch square by 3 inch long. A piece this size is about 8$ in the USA. It is available from RS or Farnell in UK but expensive. Used in university labs also.

Jim

"This is fine in practice, but will it work in theory?" (Mechanical Test Engineer)

Jim

Hello all

When facing, provided that the spindle speed used is somewhere in the right ball-park, the surface speed of cut will be higher than optimum (for the material/tool/cut/feed/lubricant etc combination) at the outside diameter, and lower than optimum at the centre. At some radius, it will be like Goldilock's porridge. At this point, the surface finish will be the best optainable, and will be visible on the faced surface. This is called "Whittaker's Ring" and well known to older manual machinists, who in practice modify the feed rate by feel and sound to obtain the best result over the whole face. Bit like riding a bike.

Works for steels but not very apparent with free-cutting materials, don't know about non-ferrous.

Jim

Hello all

I use this chair from ikea **LINK** which has the advantage of being foldable. Mine is in silver/black to match my hair and occasional mood, but there is also a cheaper version in natural wood colour.

Jim

Hello all

Further to my gear post, the ME article title was "Gear Cutting with the Shaper" and the author was "Base Circle", not "Duplex"

Jim

Hello all

Geoff; the original article was in ME September 14th 1950. If you don't happen to have that issue to hand (!) it is reprinted on the website of the New England Model Engineering Society (neme-s.org)

Russel: I wish! My gears were chewed up, I think it had been run with no oil at some point. The engine now has a rebore and crank grind (not by me, Hargreaves Engineering in Carmarthen, excellent old fashioned Engineers sadly now defunct), but I did the rest including reground camshaft bearings, line bored bronze camshaft bearings in block, head reground, new valve guides, crankshaft rear seal etc. You may know that the camshaft centre bearing on these engines was prone to wear, was the first port of call for the oil from the pump and was machined in the block, not lined.

Andrew, Roderick: I think you are right, looking back at my notes (from over a year ago when I started experimenting), it was the 20 degree angle that gave root undercut for gears with low tooth count, 30 degrees gave teeth that were too narrow on the tips and in the root. Gear pumps have different tooth form requirements to transmission gears, needing a good volume in the root area to carry the oil around, and a wide tip to minimise leakage from tooth to tooth, but the stresses are low so no requirement for a large root radius. My try-outs were just three teeth and axially short so not too time-consuming to do. The rack-shape tool is very easy to make and modify.

Andrew: Correct, the tooth flank is a series of flats. Each flank had about 25 increments of cut (final strokes were three repeats of same cut) and feel very smooth. Under my low power microscope you can't see actual flats, just longitudinal planing marks. The gears rotate smoothly and no doubt will improve with running.

Thanks all for your interest.

Jim

This took me a bit longer than a day, but I finished today

Gears for the oil pump on my Morris 8 engine.

The gears are 11DP 25 degree pressure angle in EN8. They were generated using my shaper with a rack-form tool and a fixture based on an article by "Duplex" in ME many years ago. The gear blank is rotated as the rack tool is moved laterally, using a wire drive onto a disc of a diameter equal to the pitch circle minus the wire diameter. This generates the correct involute, none of that compromise shape that you get with a shaped gear cutter. The calculated pressure angle from measurement of the old (worn out) gears was 30 degrees but this gave unacceptable undercutting of the tooth root, a problem often found on clock pinions.

11 teeth, 20 cut-increments per tooth,50 strokes per cut, X2, plus several experiments made for about 25000 shaper strokes. I made an abacus to keep track. Good job I'm retired!

Jim