Member postings for Andrew Johnston

That's the wrong approach; grind the tool to whatever shape is required and add shims to get the tool on centre height.

With regards to parting off tools one can buy 1/16" x 5/16" HSS blanks from Arc. I use similar blades on my repetition lathe:

With regards to insert parting tools i use one on my centre lathe. I found that they chatter badly if the feedrate is too low. I part off at several hundred rpm upwards and use a minimum feedrate of 4 thoui/rev, more usually 6 or 8 thou/ rev. I'm also in the part off using power crossfeed group.

Andrew

The cross slide determines the total travel, but where that travel is relative to the work is not well defined, and in practise is set mainly by the position of the tool. You may well have to swap between a LH boring bar for the rim and a RH boring bar and normal knife tool for the centre boss and bore. That is what I had to do on my 16" flywheel on a 13" swing lathe (18" swing in the gap) with a cross slide travel of 7.5":

Andrew

I didn't say it was hard, or difficult, but a PITA. Making it from solid means that 3 three points have to be marked out and then picked up on in the 4-jaw chuck. Presumably the 3/16" spigots need to be concentric, so need to be picked up to a high degree of accuracy. Drilling a hole and silver soldering in a pin is simpler and guarantees concentricity. A sliver soldered pin will be as strong as solid.

Andrew

It would be a right royal PITA to set up and machine the three spigots in the correct places. I would machine the basic block to size and then drill through for the 3/16" spigots, plus a blind hole for the 1/8" spigot. Then silver solder in a length of rod for the 3/16" spigots and a shorter one for the 1/8" spigot.

If it was felt necessary to stick with a Whitworth thread form I would screwcut it rather than try and find a LH tap. Alternatively I would make the thread M10 for which LH taps are readily available, albeit at a price.

Andrew

Roy, I'm afraid you missed my point. The implication is that the set of new weights needs to be able to weigh from 1 ounce to 4 pounds in 1 ounce steps. But that is not explicitly stated. Instead it says anything from 1 ounce to 4 lbs, in which case 1.5 ounces is valid, as would be 1.25 ounces or 1.75 ounces, in fact an infinite number of weights.

Andrew

The problem is incompletely specified, what about weighing 1.5 ounces?

Andrew

Oh my word, an outbreak of practical engineering.

I don't sweat over tool height, just line up by eye against a tailstock centre. A few thou here and there makes little difference. The smaller the work diameter the more accurate the tool height should be, but I rarely turn much under 1/4" on the centre lathe.

Probably 75% of my turning is done with two tools, a CCMT insert and a parting off tool. For these tools I keep the appropriate shims with the holders. Boring bars, profiling and HSS specials are shimmed as needed. Doesn't take long and specials might only be used once, so no point in having a dedicated holder.

I tend to run my lathe to the limits in terms of speeds, DOC and feedrates, so prefer the better rigidity of a 4-way toolpost.

Just to show that I'm not completely anti QC toolholders I do sometimes use a Dickson QC toolpost, as it is what the hydraulic copy unit came fitted with:

Note the radial spline on the left where the 4-way toolpost sits. It allows repeatable indexing of the normal toolpost every 9°; another reason I wouldn't change to a QC toolpost.

Andrew

I wouldn't, I use the 4-way toolpost that came with the lathe. My lathe is 12" x 40" so similar size.

Andrew

I don't use cutting oil or tenons on the vice, ergo no problem.

Andrew

Cost; a moulded nylon gear is much cheaper to produce than cut metal gears.

Andrew

I'd be looking for a new sparky. It may well be far to expensive to connect a 3-phase supply but I can't see the distance being a problem.There may well be 3-phase in the street anyway, so the distance to 3-phase would be a lot shorter than to the sub-station. That's what I have, a true 3-phase supply connected to the 3-phase cable buried the other side of the street.

The use of a VFD gives you the advantages of a 3-phase motor even though only a single phase supply is available.

Andrew

It takes me significantly less than 5 minutes to align my vice just using a DTI. Although my machine vice has slots milled underneath I don't use alignment blocks, as the vice gets moved between three different milling machines. Although all T-slots are nominally 5/8" they vary slightly from machine to machine.

Andrew

Make a plate of the same thickness as the wanted screw length. Drill and tap 8BA holes, insert screws and file to length. The end of the screw is automatically cleaned when the screw is unscrewed.

Andrew

The metric system is not rational but arbitrary, the same as any other thread system (except possibly BA which is based on a geometric sequence). Before, and during, WWII the French and German metric thread systems were different below 6mm OD. For instance the French used M3x0.6 rather than the international standard 0.5mm pitch. Use of M3x0.6 is still part of the JIS system in Japan, as I discovered when I made some new parts for a guitar for a friend of a friend last year.

Andrew

The OP doesn't say the gauge is 13tpi. The letter G usually refers to BSPP threads. Sometimes the nominal imperial size is approximated in millimetres. So I expect the gauge is for 1/2" BSPP. May be the OP can tell us if the gauge is 14tpi?

Andrew

Not true. In autumn 2019 a mate and I took our gliders down to Talgarth (in the Brecon Beacons) for a few days of ridge running. My mate has a Tesla and he towed his 18m glider from Bideford to Talgarth, about 75 miles, on around half full charge.

Andrew

Two orders of magnitude.

Andrew

A few tens of thou, not a few tenths.

Andrew

That opens another can of worms. Should the rollers be hardened or left soft? Same applies to filing buttons, hard or soft?

Andrew

Turn down the end of the bar to the required diagonal dimension, minus a few tens of thou. Then file the flats. Since the starting diameter is slightly smaller than theoretically correct, a small chamfer should be left on each corner. Keeping the chamfers the same size, and parallel, will ensure that the flats are just that, flat and parallel to the opposite face. Shouldn't take more than a few minutes.

Andrew