Member postings for Andrew Johnston

High performance cars, especially racing cars, have been using on plug coils for some years. It saves the complication of a high-voltage distributor and is better for EMC.

Andrew

Having been to a traction engine meeting yesterday and got thoroughly depressed 'cause the other wheels on display were a damn sight better than mine, I decided to abandon work on the engine today and give the Britan repetition lathe a run for its money.

I've only cut a thread on the end of a rod, but it's a start! Here's the set up, 1/4" steel rod (EN3B) in the dead length collet and a 1/2" Coventry diehead in the second tailstock shaft:

Spindle speed was about 112rpm and the tailstock was hand fed up to the stop, at which point the diehead carries on a bit and then pulls off. I like Coventry dieheads; when they're set up correctly they produce really nice threads:

The thread is 1/4" BSF. Now I can churn out all the studs for my traction engines. It's only a small step, but the journey doesn't begin until you've made the first step.

Regards,

Andrew

They're often an aluminium/copper alloy, eg 2024. The rivets are solution heat treated before use. This involves heating, soaking at temperature, and then quenching in cold water. This forces the copper into a solid solution. Over time, usually days, the copper migrates out of solution and ends up on grain boundaries, making the rivet harder. This is age hardening.

The yellow/green finish is an etch prime, used to be zinc chromate based, but there are chromate free products available now. I'm pretty sure we used to use a zinc chromate goo when assembling steel fittings into wooden aircraft, to prevent corrosion.

Regards,

Andrew

Ideally by the neck..............

Andrew

Neil: Thanks for the information on the gears. I'll have to read up on the parallel deptth method, as I need to make some small bevel gears for the governors on my traction engines.

I could take out the splines in a series of steps, but I'd still like to finish with a full width cut. I want the outer edge of each spline groove to be circular so as to exactly match the crankshaft, rather than square. I guess I'll have to suck it and see.

Regards,

Andrew

PS: Sadly I don't have an EDM machine lurking in the garage, at least not yet.

Edited By Andrew Johnston on 18/11/2012 21:07:41

Jason: Thanks for the insights. I'll rephrase the question. I have a slotting head on the back of the Bridgeport, which is fine with a 1/4" wide keyway in cast iron. My prevarication is due to wondering how it is going to cope with a 5/16" wide spline in EN24T? And more to the point, if it cannot cope, will it simply stall, or will I end up badgering it?

Regards,

Andrew

Neil: Thanks, I was wondering. I'm not sure how one would independently measure the position of the table, versus the dial reading. May be a test indicator on a bar on the table? If the angular changes are small enough I guess one can ignore the arc versus straight line errors.

The gears look fantastic; are the bevels parallel depth? How did you cut the splines on the pinion? I need to cut some splines for the gears that slide on the crankshaft for my traction engines. I'm prevaricating, which means I'm not sure how to go about it! The only thing is, I think the pinion shown has more than 13 teeth, surely not a dividing error!?

Regards,

Andrew

Ian, Neil: I admit it, I'm being an idiot. I agree that the relative accuracy does not change as the gear gets proportionately larger. I'm not quite sure what I was trying to say!

As far as machining my final drive gears go, I did the sums as follows. The gears are 5DP, 72 teeth with an OD of 14.8". My dividing head has a quoted maximum error of 1 min 30 sec. I'm making an assumption that my industrial 12" rotary table is similar. I make that a maximum error of about 3 thou on the circumference of a 14.8" disc. So the tooth width could be 3 thou wider, or narrower, than theory. The rule for cutting deeper for one gear of a pair, with 20°PA, is backlash times 1.46. So that means I need to cut about 4-5 thou deeper than normal.

Neil: I am intrigued as to how you measured the maximum error on your rotary table?

Regards,

Andrew

In a word, no. If you're above base speed of the motor, then yes you will get constant power. But below base speed you will get constant torque, but since the speed is deceasing so will the power.

Let's take some easy numbers. Assume a 1hp motor with a base speed of 1500rpm at a frequency of 50Hz. If you run the motor at 100Hz, you'll get twice the speed, but half the torque, so still 1hp. However, if you run at 25Hz you'll get half the speed, but the same torque, so only 1/2hp. To some extent it is possible to increase the current, and hence torque, below base speed but you then run a serious danger of overheating the motor. Remember that industrial 3-phase motors are dwsgined to run hot at their design speed, often over 100°C.

Regards,

Andrew

More like green light? - Andrew

The OP says that his rotary table has provision for dividing plates, so why not use them? Also, we do not know the diameter of the gear to be cut; the bigger it is the more accurate the division need to be.

I will be cutting my traction engine final drive gears on a rotary table, as per Richard's setup, as at 14.8" diameter they will not quite fit under the milling machine arbor. I am budgeting for an error of 2 thou at that diameter and will compensate for it by cutting the teeth slightly deeper. That's accuracy of course, not resolution, which is quite a different thing.

Regards,

Andrew

I don't see why not? If you hook up a 415V rated star connected 3-phase motor to a 240V phase-to-phase supply it will run. The speed will be the same, but the power available will be reduced, by 1/sqrt(3) in theory, exactly as Dave says.

In the original post Dave says the motor is two speed. Presumably the motor runs in star with 'n' poles, and delta with '2n' poles, so that at the slower speed you get about 86% of the higher speed power rather than 50%.

Technically the 240V and 415V UK supplies are the same, it's just a question of where the voltages are measured.

Regards,

Andrew

Mark,

I agree. The rationale is as follows. To make one full turn of the rotary table takes 90 turns of the handle. To divide a single turn of the table into 53 equal parts we need to turn the handle by 90/53 each time. Since 53 is a prime number we cannot simplify the improper fraction. However we can express it as 1 and 37/53. If we have a 53 hole plate then it is simple! Here's a picture of a 63 and 69 hole plate I made for my dividing head, to cut 63 and 69 tooth gears, because I was too idle to set up the gears for differential indexing:

Remember that any errors in the dividing plate will be divided by 90, which is good.

Regards,

Andrew

Hi Dave,

So that explains why the tailstock lock is in the collet tray. Surprisingly I've run out of questions at the moment. I'd just like to say thank you very much for all your help and advice. It has been most interesting and useful. Unfortunately work has caught up with me, in the sense that I need to get down and do some! I'm not sure when I'll get a chance to use the Britan for real, but when I do I am sure that will result in more questions.

Regards,

Andrew

PS: I've sent you a PM

Hi Dave,

Thanks for the tip on the stop with a secondary shaft; fortunately I do have one. I had noticed the missing shaft lock. For some reason it is sitting in the wooden collet rack along with the tailstock capstan collets. I do not know why it was removed, unless it had a reputation for getting in the way if it wasn't being used, or had a tendency to fall out if a shaft wasn't fitted? Which of course raises the question, when was it used? Presumably it locks the second shaft, the one with the black knob? The only time I can think it would be used is if the shaft contained a centre for supporting long work?

Regards,

Andrew

All my metric drills (Dormer) are TiN coated; the coating doesn't seem to wear off even after hundreds of holes. I don't know whether this would be true for lower cost cutters.

The question of re-sharpening coated cutters doesn't really apply. For small cutters it simply isn't worth resharpening. I was talking to the salesman at the industrial tool shop I use on Friday. He was saying customers always ask for a discount on cutting tools. His point was that since the cost of the cutting tools is about 3% of production cost why bother with a 10% discount. A lot of commercial machining is done with CNC machines so if you use a resharpened cutter not only do you have to pay for the resharpening you also need to especially set the machine for that particular cutter diameter and length. Cutters are made for industry, the ME fraternity has to use what is available.

And before anyone jumps in about industry versus ME, I do have a fairly well equipped Clarkson T&C, but it simply isn't worth me sharpening small cutters. I've got better things to do with my time.

Regards,

Andrew

Edit: D**n, Terry beat me to it!

Edited By Andrew Johnston on 11/11/2012 14:46:24

Edited By Andrew Johnston on 11/11/2012 14:47:16

There's also TiALN - Titanium Aluminium Nitride. This is harder than TiN, but requires high temperatures to function correctly. The theory is that as the temperature rises the aluminium forms aluminium oxide more easily, which is very hard, and which then also prevents further oxidation. High temperature means running the cutter dull red, so no coolant! The coating is intended primarily for cutting harder materials with no coolant, just an air blast to remove chips. I use TiAlN coated end mills for cutting stainless steel and gauge plate.

Thinks: Might be worth trying a TiAlN cutter on HSS to see if it's any better than plain uncoated carbide.

Regards,

Andrew

Hi Dave,

Thanks for the information on knurling. Is this the black knob you mean?

I've got one of them, although presumably it can be moved between shafts, or I could make some more.

Regards,

Andrew

KWIL: Yes, but! I'm not sure I've ever used a caliper knurling tool; if I have it would have been at RAE Farnborough back in the 1970s. Hence the question.

Regards,

Andrew - hot 'n' bothered, having spent all afternoon trying to weld the rolled rims for my traction engine wheels, give me some nice machining any day of the week.

Hi Dave,

Using spiral flute taps makes sense. I've got a pretty good range of metric spiral flute taps, and a few imperial ones, so shouldn't be a problem. However, I suspect that trying to find ME taps in spiral flute form might be a bit tricky! I can't see a need for left hand threads at the moment, but it is good to know that it's a relatively simple modification, should I need to do so in the future.

I expect that I'll need to get to grips with back stops fairly quickly, as one of the first things I'm planning to make on the Britan are all the studs I need for the cylinders on my traction engines, all 1/4" and 5/16" BSF.

Now onto knurling; here's the knurling tool and a few spare knurls:

It's unfortunate that a couple of the knurls seem to be singles, but that's life. At least knurling wheels are readily available. It seems clear how the knurling tool works, in principle at least. The two screws and nuts at the sides of the tool are used to swing, and set, the diameter of the work for the knurling wheels. However, any practical hints on how to knurl will be most welcome. Presumably the knurl wheels are set to form the knurl in one pass? I assume that some experimentation is required?

Regards,

Andrew

Edited By Andrew Johnston on 10/11/2012 11:31:57