Member postings for Andrew Johnston

It's not easy to measure the working end of a drill bit, but it should be better than 0.01mm. On my Dormer drill sets the shanks (easier to measure) are 0.01/0.03mm smaller than nominal size as the drill bits are ground on a slight taper. There are two rules for buying cutting tools:

Rule 1: Don't buy cheap cutting tools

Rule 2: See rule 1

The cheap sets at a 'good' price are nothing of the sort. If they're poor quality then any price is too expensive.

I stock up on my drills once or twice a year. All cutting tools wear and need replacing, although I drive my tooling fairly hard. In the smaller sizes the Dormer A002 drills are fairly cheap so although I have the wherewithal to sharpen them, it's simply not worthwhile. I'd rather spend the time making parts.

Andrew

Been making studs and the slidebar side clamps for my traction engines. The slide clamps are not functional, but are a prominent feature on the fullsize engines:

And here is a clamp in situ with the recently machined rear cylinder casting and home msde studs and nuts:

So far everything slides together nicely without shake and no need for shims.

Andrew

Can't argue with that assessment!

Andrew

JasonB: Errr, I'm not about to rush out and buy a mill from Arc; don't really need a fourth milling machine. Anyway, I'm probably on Ketan's no sell list as an awkward customer.

Agreed that on the CNC mill I tend to run smaller cutters at faster speeds than I do on the Bridgeport. Partly because the CNC mill is VFD/motor so slow speeds mean a loss of power. The Bridgeport is limited by power (1.5hp) and lack of rigidity. But I can still run it to maximum power. When I get time I'll try faster speeds on aluminium. The horizontal mill is feedrate limited, but it's till possible to take cuts in steel that use all the available power (5hp). Seems fine with a geared drive on interrupted cuts. I guess it depends upon the quality and type of gear.

Andrew

That'd be me then. No idea how you manage to translate stalling the mill due to be over-ambitious into a problem with belts and 3-phase motors.

Andrew

Never seen one. Assuming this is a one off clean up of the face on an ISO30 arbor for a mill simply put the arbor in the mill and clean up with a lathe tool clamped to the table.

Andrew

As I would expect a careful study of the drawing shows that the central slot is slightly deeper than the slot itself. So cut a slot slightly deeper with an endmill or slotdrill and then use a T-slot cutter. Cutting the central slot slightly deeper stops the T-slot cutter from potentially cutting across the full width on one side.

Andrew

I change feed rates on a regular basis, if only because the cross feed is half what is set for the axial feed. For most general turning I use 4 thou/rev. Very occasionally I'll drop down to 2 thou/rev, but have never used the lowest feedrates.

When roughing I up the rate to 8 or 10, or higher, thou/rev depending upon material and depth of cut. An increased feedrate can also help with chatter when boring.

Andrew

Don't pussyfoot around, give it some welly! If nothing else with a VFD drive you'll have more power available. As an example I was turning this flywheel at 60rpm:

But it is over 16" in diameter.

Andrew

Definitely not right; to be technical it's chocolate teapot territory! Looking at the lathe specs it has a 2hp motor, so as a rough rule you ought to be able to remove about 2 cubic inches of mild steel per minute. Would I be correct in assuming that the lathe has an induction motor and VFD? If so I suspect you need to up the speed, you might have full torque at 200rpm but the power will be well down, irrespective of the feedscrew clutch tripping. We don't know what diameter the work is, but 200rpm seems very slow for steel and insert tooling.

Andrew

This is the sort of finish you ought to be able to get on brass with insert tooling:

The part was turned with ordinary CCMT inserts, not the ground and polished ones intended for aluminium. The threads were screwcut using inserts too.

I'd say there's something wrong with the leadscrew clutch if it jumped out when turning brass. I'd expect the clutch to be set to drop out just before the spindle motor is overloaded. Otherwise there's not much point in having the extra motor power if you can't use it.

Andrew

Two issues; first how do you know that a skim will produce a "zero" result? And second cost, it would be time consuming, and hence expensive, to do.

As Jason says the spindle should be hardened, which makes it more difficult to turn. Will the cross slide travel in a straight line perpendicular to the spindle axis to considerably better than 5um? Probably not, and the cross slide should turn from parallel to slightly concave. So it may not even be aligned.

Manufacturers aim to make parts to fit together to achieve an acceptable level of accuracy without the need for fitting on the job. Didn't the original Myford do a lot of fitting, with it's attendent costs? I wonder what happened to them?

Having said all that I have skimmed the nose of my Bridgeport spindle:

But it was out by a lot more than 5um. Of course in normal use the run out on the nose doesn't matter. But I make extensive use of the Tormach TTS tool system which relies upon the spindle nose to provide consistent positioning for tool length calculations. If the spindle nose isn't true then the tool wobbles.

Andrew

Jason is correct, that's one hell of a countersink! For the dummy rivets on my 6mm thick hornplates I just did a couple of turns with a taper pin reamer and a couple of clouts with a hammer per rivet.

Neat riveting though; I always seem to end up with hammer marks in the wrong place.

Andrew

I buy from Drill Service in Horley.

Andrew

By coincidence the last thread I screwcut was M16x2 in EN16T, for a cutter drawbar. The finish is ok, but since I was cutting a metric thread on an imperial lathe I couldn't use my high speed threading attachment. I was running at slow speed, 85rpm I think. Here's the thread:

The thread is better than it looks, and works fine.

Andrew,

OP says he doesn't know what the steel is, so it's a crap shoot.

The standard way to harden high carbon steels is to heat to around 800°C and hold for one hour per inch of thickness. Then quench in brine and agitate while doing so. If you don't agitate you'll end up with a hardness around 40Rc instead of the wanted 65Rc, or thereabouts.

To temper heat to the required temperature (a couple of hundred degrees or so depending upon application) and hold as for hardening and then quench.

Of course one could just heat to red and then piss on it and hope the nitrogen compounds give a form of nitriding!

Andrew

Sometimes, on steel. Haven't seen it on cast iron or brass. I start with large depths of cut,up to 20 thou depending upon the thread pitch, and reduce DOC once I'm close to full depth. For stringy materials like steel it's possible the swarf on the first cuts rubs against the flanks as it tries to escape. With smaller DOC the swarf is smaller and thinner, so more pliable, and will have less of an effect on the flanks. For brass and cast iron where the swarf is fine particles the issue doesn't seem to occur. I do all my screwcutting by plunging straight in.

Insert profiles are rather more involved than DC31k propounds. Here are three inserts:

Which are full form and which partial?

The one on the left is marked 16ERAG60, so a partial profile for a 60 degree angle thread. The middle insert is marked 16ER-8W, a full profile insert for 8tpi Whitworth, where the partial tooth does indeed form the rounded crest, as specified in the Whitworth form. The righthand insert is marked ER16-2.0ISO, a full profile insert for 2mm pitch ISO threads. These threads have a flat crest, so the second tooth is not needed to fully form the crest, a flat is sufficient.

Andrew

I've just bought a long series 1/2" reamer for a part that is about 7" long. Longer than that and I suspect you're into specialised (equals expensive) tooling. Best bet would be a gun drill, but ideally they need thru drill coolant at considerable pressure and are not simple to set up. A D-bit will probably sort of stay straight, but there's going to be a very long length of D-bit that is a close fit in the final hole. That's a recipe for something seizing.

Personally I'd explain to the client that it's going to cost him x pounds more per part and does he really want to cough up the extra readies?

Andrew

That's what I do, at least to get an initial number on the cross slide to aim for. I find a quick brush of the thread helps before trying the mating thread. It's particularly helpful for dusty materials like cast iron. It's surprising how little dust is needed between won't go on and a rattly fit.

Funny thing, but I've just bought M10x1 taps and die. The internal threads on the steam head for my traction engines are shown as 3/8" by 26tpi, aka British Standard Brass (BSB) thread. While taps and dies are still available they're not especially cheap. I'll be making the mating parts with external threads rather than use the commercial parts listed on the drawing, so no need to stick to BSB. The M10x1 thread is pretty close, the taps and dies are less than half price and best of all a spiral flute tap is available. So I only need to buy one tap, not a set of two or even three.

Andrew

Wrong question. No single mill will do everything well, so you need more than one. Same for lathes, you should have more than one.

Andrew