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Member postings for Roger Hart

Here is a list of all the postings Roger Hart has made in our forums. Click on a thread name to jump to the thread.

Thread: Overload trip
09/02/2019 10:35:52

You might like to try the small synchronous motors used in central heating diverter valves. They are designed to operate stalled (and get a bit hot!) without burning out. In the stalled mode there is usually a resistor and a diode in series with the motor. They are internally geared down a lot so operate at a civilised speed.

These motors are pretty cheap in the usual place and come with a small pinion and have a useful torque.

Thread: Is it a drone?
04/02/2019 12:39:48

Interesting.

I bought a flapping bird toy from China. About £10 and includes radio, motor flapping mechanism etc. Works but not as good as the Japanese effort. Thought I might have a go at using the bits to make a better one. The Dellfly project looks interesting www.dellfly.nl/nimble and includes links to code and control system hardware.

so many interesting things to do and so little time.

Thread: Mystery optical device
03/02/2019 09:56:35

I found something like that in a box of old vidicons, pcbs etc. Inside the bigger triangular box are a couple of front surface mirrors and a dichroic block like one shown. I got it for the input output lends units (nice eyepieces). The block shown is 50mm on a side and carries two pretty coloured bits of glass. Basically it takes in an image, splits up the colours and shoves out 3 beams to the vidicons.

If anyone wants the dichroic mirror block shown you can have it, just a PM.

p1040243.jpgp1040242.jpg

Thread: Dial Gauge Advice
31/10/2018 11:09:06

I agree that the DTI is a good first choice. I got a 0.001 inch one at a boot sale many years ago and it is the most useful I have. It is robust, useful travel and not too nit-picky. For most jobs this is the one.

I have a couple of much better DTIs and a finger type gauge, but they are a d%^n nuisance to use with the needle going round several times until you have got the work nearly central. In this case posh is not necessarily better unless you want real accuracy and that is whole ball of wax on its own.

Thread: Astro Compass back into use
07/10/2018 09:35:15

Recently dug the top half of this astro compass out of the junk box and made it functional once more. Handy for finding out if some planet or other is visible between the trees that mostly block my south view.

I always thought you would have to be in pretty dire straits to need to use one of these.

By way of confession, the bottom half got made into a harmonograph about 55 years ago.

07/10/2018 09:30:15

p1040197.jpgp1040196.jpg

Thread: ML10 - ready for the boneyard?
31/07/2018 14:45:20

Oh dear, just spent 2 days fitting a new leadscrew to my ML10 and read this post. Took a straightedge to the bed and lo and behold there is light to be seen. An imperfect Myford!; off to the scrapyard with it.

All those gearwheels and clock bits and optical parts and the odd steam and IC engine. All tainted with imperfection, all have to be recalled and scrapped. Well probably not, for it is a poor engineer who blames (his) tool. Some may need perfection but for most model stuff I doubt the odd bit of imperfection in the lathe is going to stop a semi competent engineer. Indeed for me dealing with the quirks of older equipment (including mine) is half the fun.

More realistically it would be interesting to know what the real options are for a regrind if only to help my heirs flog the thing because I doubt I will be going to the bother.

Thread: Dropping 12v dc to 6v dc
27/05/2018 16:37:25

Beg pardon for assuming this was some kind of Dynastart system. To assume is of course to make an ass of u and me.

However I wondered what had led you to the 'high amps' part of the requirement. Is there something a bit odd about the trembler coil? I used to have an old model T coil and that was pretty low current (but fun). Just for scale 'high amps' to my mind is 20 amps or more but of course to some people 10 milliamps may seem a lot. Around 1 amp seems about right for the sort of trembler coil I think of.

I suppose a worry is over voltage on the trembler coil wrecking the high voltage insulation. Hence the 6 volt battery, OK but a bit of a nuisance. My only worry with a buck converter is the failure mode, does it go short circuit and hopefully blow a fuse in the 12 volt line or does it end up passing the 12 volts straight through.

Perhaps you might get rid of the battery and replace with a good sized capacitor - say 30,000 microfarads shunted by a 7 volt 5 watt zener diode, they tend to fail short circuit. Even quite respectable designers use zeners like this as a backstop against the failure of series regulators.

Anyway, good luck with the vintage motor.

26/05/2018 14:16:32

I would respectfully suggest this job is more difficult than it looks. To swing the 6 volt 'motor' requires high amperes of the order 200 to 300 and there will be some vile current waveforms and spikes as it turns. Really only a 6 volt battery can handle that and a fairly meaty one at that. Then comes the charging of the 6 volt battery from 12 volts. A simple dropper resistor is probably not so good here. Something is needed to regulate the 6 volt battery charge. Possibly the mag starter has the necessary to do that, maybe not.

Thread: Wilding Hipp Clock Toggle
07/05/2018 10:44:40

Many years ago I looked after clocks in a telephone exchange, just like the one pictured above. The maintenance schedule advised that the Hipp clock be oiled once in a blue moon. In my youthful enthusiasm I decided it was about time, older hands advised 'leave the b%&*dy thing alone'. I spent the next couple of months resetting clocks and trying to get the thing back into time, the old hands were right!

FWIW the toggle was steel and pivoted very freely.

Thread: Turning paxolin
19/04/2018 17:17:35

Been making a couple of disks from 1/4 inch paxolin. The tool traverses from right to left and as it leaves the left hand side a small amount of delamination takes place. Not serious for this application just not a tidy job. But how do I avoid this happening - turn from each end towards the middle perhaps. Or is there a better way?

Thread: Advice Repairing Opera Glasses?
04/03/2018 15:58:19

I would say you have got a job on with this one. I agree the lens should be accessible via the serrated sleeve. The snag is that the brass is v thin and the threads fine so any jolt will tend to cross a thread or put the sleeve out of round. I would cautiously grip the edge of the sleeve with a stumpy nose plier and use that to try and undo in the usual direction. Don't overdo it or the sleeve will tear or cockle up. That should free it up till it is finger free. Maybe a taste of light oil before you start.

The eye-piece pressing looks more problematic. My guess is that it is a couple of pressings soft soldered together. The snag is that if you take it apart and re shape it then it will be hard to put it back together any sense. To say nothing of re colouring it. Short of facing that problem I would look to making some sort of shaped stake to go inside and try and 'encourage' it back into some sort of correct shape without doing further damage. As I said, this looks a right job, good luck.

Thread: G. Boley watchmaker lathe
21/01/2018 12:15:17

I use a 6mm lathe so a bit smaller. I found sewing machine motors have an annoying high pitch whine, so I use a small (1/20th HP) induction motor about 1500rpm. This has a 2 step pulley - about 75mm dia and 30mm dia. Add a bit of cotton string and the 3 pulley settings on the lathe and I find that works well without that awful noise.

Motor sits on a heavy baseboard and lathe has a heavy iron base, so it is easy to adjust the maximum torque by pulling or pushing on the base. The same arrangement using a length of cotton and a clamp-on pulley works for my home-brew turns.

Thread: Refurbishment of Antique Aneroid Barometer
19/10/2017 10:46:32

Before you start I would think very carefully. You cannot patch up lacquering, it is an all or nothing operation. I used to do up clocks and getting the old lacquer off was sometimes easy(ish) but most often it was the very devil of a job especially on not so antique not so good items. Often only hard work on the polisher would do it. This approach is not so good if the original finish was grained. Or see the emery stick approach above.

So try a small area with your chosen remover, you may be lucky.

Also, putting shellac lacquer on by hand is not so easy. The usual advice is to warm up the work, use your best sable brush and don't go over the work again. If you leave any places it will dull and look bad later on. If you go too slowly it will dry as you go and drag.

Thread: Making a Potts drill jig bracket
12/10/2017 17:13:21

p1040097.jpgI found a Potts drill grinding jig a while back but the mounting is a bit of brass angle, not the usual bracket. See pictures.p1040096.jpg

The pictures I have seen of usual bracket show a slotted plate with some sort of cube to which my jig would bolt. The question is - is this cube fixed at 90 degrees or is it adjustable?

Thread: What Did You Do Today (2017)
10/10/2017 15:48:22

My expensive hedgecutter started playing up, lousy starting and wouldn't pull the skin off a rice pudding. New plug then fiddle with carb - no change. Now I hate carburetors so ordered a replacement on fleabay £5. Fitted and now runs a treat - result.

But for one thing. When I fitted new carb I found the throttle cable was slack and needed a twiddle on a hard-to-find adjustment to make it OK. So now I am left with the guilty feeling that I didn't need a new carb at all, just to use my eyes and what passes for a brain. Probably all that was wrong was that vibration had slackened the throttle cable adjustment. So should I put the old carb back to verify or should I leave the bl&*dy thing alone.

Thread: cleaning stainless steel
13/08/2017 16:45:25

Thanks everyone. I tried electrolysis with citric acid. I used a stainless rod as a cathode to the -ve supply and the workpiece to the +ve. Passed about 200mA for 4 hours and the grey/black muck shifted and left a smooth grey surface. Not a shiny result but a bit better, the hard grey/black surface has gone. A good taste of the buffing wheel looks in order.

I looked at electropolishing but was a bit windy of conc sulphuric + conc phosphoric and for a little job like mine not worth pursuing.

12/08/2017 09:53:18

Been doing some silver soldering of stainless and this has left a greyish film over the work. I will probably have to clean up using W&Dry but I wondered if there was any easyish way to clean up stainless. The usual sulphuric pickle doesn't work and neither does citric. I had read that HF is good for this, but not nice stuff and not available in most ironmongers....

Thread: soldering stainless steel to copper
02/04/2017 07:05:14

Thanks for the advice all. I have some Jenolite and also a tin of Fry's is lurking somewhere. Will give it a try.

31/03/2017 13:29:22

I want to soft solder (tin electrical solder) copper pipe into a stainless steel fitting for a vacuum system.

I don't know the SS grade - it came from a refrigeration supplier. I read that a phosphoric acid flux is needed but it is not obvious from looking at fleabay which if any is suitable. So, if possible a product and a source please, not too expensive either.

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