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Member postings for Andrew Johnston

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

<< First < Prev 343 344 345 346 347 348 349 350 351 352 353 Next > Last >>
Thread: Tool tips
17/10/2010 21:36:14
Paah, the whole centre height thing is a pipsqueak!
 
Regards,
 
Andrew
Thread: Scale model Economy hit & miss engine builders wanted
17/10/2010 10:26:21
I haven't made those bits yet, but it didn't occur to me to make them from anything but spring steel.
 
I bought my spring steel from Folkestone Engineering Supplies. It comes annealed, so the issue is not how to cut it, but how to harden and temper. Not a problem for me as I have an electric heat treatment furnace. I don't suppose the hardening and tempering is that critical, so could be done by other means.
 
Regards,
 
Andrew
Thread: Cutting Bevel Gears
16/10/2010 22:07:51
I'll second the book recommendation; good practical advice. I first used it in 1976 when designing bevel gears as part of a pre-university design and build project. Been referring to it on and off ever since.
 
Regards,
 
Andrew
Thread: Continuing Articles
15/10/2010 10:50:15
But you can draw what you can't build - Andrew
Thread: Scale model Economy hit & miss engine builders wanted
14/10/2010 22:51:37
Hi Jason,
 
I chose M12 as I already had all the necessary taps and dies and didn't, at the time, have any BSP threading equipment. I am not sticking exactly to the design in this area, so the availability of off-the-shelf elbows is of less concern to me than it might be to other makers.
 
Regards,
 
Andrew
Thread: Midlands Model Engineering Show at Warwick
14/10/2010 22:42:31
Hi John,
 
I'll look in on the Saturday.
 
Andrew
Thread: Scale model Economy hit & miss engine builders wanted
14/10/2010 18:44:22
Hi Charles,
 
I've eventually found the jig, hiding behind the aluminium offcuts bin. Two photos have been added to my 'Economy' album. One is of the jig and the other shows how the cylinder head was mounted. The inlet and exhaust port faces were cleaned up and tapped M6 before mounting. As you have no doubt realised the thread callout of 1/2" BSP is wrong. I used M12 instead.
 
Regards,
 
Andrew
Thread: Machinable Ceramics
14/10/2010 12:33:41
Hi Pete,
 
Thank you for the information and sorry for being slow in replying. I've been on holiday up north (down south to our esteemed editor) with the glider.
 
Brilliant idea to use Corian, I'll buy a bit from Ebay and give it a try. I had also thought about using a high temperature plastic, such as PEEK1000. Machines well and is good for 250°C. The only doubt I have is how well it will stand up to the flame front temperatures.
 
Time to stop thinking about it and get on and experiment!
 
Regards,
 
Andrew
Thread: Scale model Economy hit & miss engine builders wanted
14/10/2010 12:11:55
Charles,
 
I remember mounting the cylinder head on a piece of aluminium angle, for use in the 4 jaw chuck on the lathe. This allowed machining of the spigot that fits in the cylinder. Once this is done, the head can then be mounted in the vertical mill, with the DRO zero'd at the centre. Then all the flat surfaces can be machined and the holes drilled.
 
I'll have a go at trying to find the jig later today. If I do find it, I'll post a picture of it.
 
Regards,
 
Andrew
Thread: Using an Imperial Ainjest Threading Unit for Metric Threads
07/10/2010 08:03:15
Kilroy, as in 'Kilroy was here', in the US, Chad in the UK. As is often the way with these things the origins are somewhat lost in time.
 
Regards,
 
Andrew
06/10/2010 22:38:34
Hi John,
 
Thanks for having a look at this; I'm glad that you agree it should work! Using a reasonable count encoder it should be possible to get the spindle back within a degree or two of where it started. By using a bedstop for the saddle I guess it should be possible to get the saddle back to it's start position within a few thou. I reckon that will be more than good enough.
 
I guess my next steps are to get the Ainjest unit fitted and then learn how to use it to cut imperial threads. Then ,once I've got all the CNC milling and TIG welding out of the way for work, I can get on and try fitting an encoder to the spindle.
 
No doubt some enterprising business type will latch onto Tippex and sell it to machinists as a magic, all purpose, must have, product for the workshop at an inflated price!
 
Regards,
 
Andrew
Thread: Metric vs Imperial - Practical or Traditional?
05/10/2010 23:12:13
Not only that but the US and English inches were different until the late 1950s.
 
Regards,
 
Andrew
Thread: Using an Imperial Ainjest Threading Unit for Metric Threads
05/10/2010 23:06:40
The character is called Chad, in the UK at least, and was normally accompanied by a long suffering comment on the deprevations of WW2, such as 'Wot, no sugar'.
 
Nick: You are absolutely right. An encoder with one pulse per rev could lead to errors if you weren't careful. I was thinking of a 100, or even a 360, per rev encoder. Then a plus or minus one count error on the spindle position would be small in terms of degrees. It would still be pretty slow in electronic terms for the counting, even if the spindle was running at 1000rpm.
 
Ady: Correct, the leadscrew on my lathe is 4tpi. I can't find a 73 or 63 tooth gear in the system. My lathe (Harrison M300) has a few change wheels in the normal place down to a quick change gear box. The QC box has an eight way rotary selector plus three, three position, selectors. Metric threads seem to be associated with one position on one of the three way selectors. So there must be something clever in the QC box, but I haven't identified which set of gears yet.
 
Regards,
 
Andrew
05/10/2010 22:51:45
Great stuff, thanks John. It's always useful to have someone looking over one's shoulder, in case of me missing the obvious.
 
I haven't seen a 127 tooth gear, Myford or otherwise, but I understand that they are LARGE! My lathe certainly doesn't have one. I haven't yet worked out which set of gears it does use for the metric conversions.
 
A bit more playing with the maths seems to indicate that the key distance is 127 times the metric pitch of the thread to be cut. For instance, if the thread pitch to be cut is 1.25mm, then 127 times this is 158.75mm. But 158.75 divided by 6.35 (1/4" in metric speak) gives exactly 25. So, the spindle does 127 revs and the leadscrew does 25 revs. Given that 127 is a prime number this fraction cannot be simplified further. Since the numbers are both integers, then as far as the two threads are concerned, the relationship between the threads is the same as at the start.
 
Regards,
 
Andrew

05/10/2010 19:40:20
Thread: c.n.c .
05/10/2010 19:15:54
Errrr, I think the specification might be 36 Ncm, not 36 nm; quite a difference. Two orders of magnitude in fact. For reference the stepper motor that drives the Z-axis on my CNC mill is  1200 oz-in, about 850 Ncm.
 
Does the z-axis lose motion in one direction only or in both directions? For example if you ask the head to move down in successive 5mm steps, does it work correctly? Conversely, if you ask the head to move up in successive 5mm steps, does it work correctly? If it misses steps in both directions it may be due to friction, or stiction, in the works. If it works correctly in the down direction, but not the plus, then I would agree with John S that the stepper motor may not have enough ooomph to lift the head.
 
Regards,
 
Andrew

Edited By Andrew Johnston on 05/10/2010 19:16:35

Edited By Andrew Johnston on 05/10/2010 19:17:05

Thread: Chronos silver steel, water or oil quench?
05/10/2010 11:53:14
I don't know for sure, but the second biggest constituent of urine, after water, is urea. Urea contains nitrogen, and gives off ammonia when in contact with water. That might explain the nasty niff. Perhaps it was a early form of nitriding?
 
I don't have a lemon tree in the garden, but I have been known to micturate on the compost heap, rather than traipse back indoors when caught short.
 
Regards,
 
Andrew
Thread: Rhoestats
05/10/2010 10:13:54
Hi Ray,
 
Personally I wouldn't use a rheostat to drop the voltage, although it does have the advantage of being simple. Both RS and Farnell seem to have rheostats at rather less than £400. RS also do a wirewound 'adjustable' resistor, which might be suitable if you do not need to keep adjusting the resistance. Might be worth a look on their websites to see if they have anything suitable.
 
Regards,
 
Andrew
Thread: spindle run out
05/10/2010 09:59:42
Hi KWIL,
 
Home induction heating has been done, see the following link:
 
 
I did find a US webpage where you could buy a small induction heater for home use, but stupidly I didn't bookmark the page. And I'm damned if I can find it again. If I do, I'll post a link to it.
 
Regards,
 
Andrew
Thread: Chronos silver steel, water or oil quench?
05/10/2010 09:55:59
I second the recommendation of Tubal Cain's WPS1 book. It explains a complex subject in sufficient detail to allow proper hardening and tempering of carbon steels in the home workshop.
 
Regards,
 
Andrew
<< First < Prev 343 344 345 346 347 348 349 350 351 352 353 Next > Last >>
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