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Member postings for Dave Martin

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

Thread: 3D printers are getting cheaper
20/02/2018 09:49:22
Posted by Muzzer on 19/02/2018 22:50:31:

DLP printers are getting cheaper too. This one's £500 from Amazon and isn't any cheaper from AliExpress (they have got the pricing and suppy chain under control!).. The resin seems to be about £60 per litre.


I'm intrigued by that advertisement - I think they're mistaking 'model' and colour, as the advertisement says:

Colour: Photon

without mentioning what wavelength!

Thread: Atom Minor Mk III
05/02/2018 12:04:58
Posted by Old School on 04/02/2018 17:38:45:

.....Castor oil is a good lubricant.....

And you can't beat the smell of Castrol R !

Thread: Crayford Telescope Focuser
29/01/2018 21:54:40
Posted by Geoff Theasby on 13/02/2017 20:13:59:

That would be one of the Six Kingdoms you can see from the top of Snaefell.


Actually, Geoff, we always say it is seven kingdoms:
England, Ireland, Scotland, Wales,
Neptune's, and
Mann itself

Edited By Dave Martin on 29/01/2018 21:55:32

Thread: A really oddball twin lead M6 bolt wanted
20/01/2018 20:52:53
Posted by Ian P on 20/01/2018 14:38:52:

This is to replace an existing damaged bolt on an imported bit of camera mounting hardware (dovetail plate and clamp) which fits on Tripod for easy camera swapping.

The damage was caused by me not realising is was a two start thread when trying to remove the locking compound with a standard M6 Die.


Ian - could I just interject - are you sure it's M6? only reason for asking is that the vast majority of the actual camera and tripod fittings are either 1/4 (UNC if I recall correctly) or 3/8.


04/01/2018 09:20:37


unless you can see it running, would suggest you factor in cost of possibly having to replace the spindle and feed motors + possibly any contactors etc.


Thread: Starrett Tool Makers Steel Clamps
28/12/2017 08:34:25

Stew - PM sent


Thread: Any uses for damaged cutters?
18/12/2017 14:15:26


I can't quickly find the thread, but I think it was on here - someone recently showed the use of slitting saw blade as a parting tool, and when a tooth was blunted, the blade was just rotated. The question was asked though as to how well swarf would be cleared from the cut....


Thread: A dongle dingle
18/12/2017 14:09:38
Posted by Neil Wyatt on 18/12/2017 13:59:15:

This will cost you less than £3, you can remove the sockets from the plug shell (by depressing the little tag) wrap them in tape and attach directly to the right pins on the 25-pin connector. Seal with Sugru.


Edited By Neil Wyatt on 18/12/2017 13:59:26


All of that is fine - but we're still waiting for Sam to confirm if it really is RS232 (pretty unlikely) or it is a parallel port dongle (which the vast majority were).


18/12/2017 10:47:14
Posted by peak4 on 18/12/2017 10:37:04:

.... Does the physical dongle have gold pins or pin sockets on?? .....

Bill - I suspect, if looked at in isolation, the dongle will have both male and female connectors, as most were designed to operate in pass-through mode, and at least one of those I have doesn't have the PC or printer sides marked, it just relied on the polarity of the connectors to ensure it was plugged in the right way round.

Sam - what would help is if you can get a photograph of the port on the back of your laptop where your dongle does work - just the port without the dongle plugged in.


18/12/2017 10:16:39
Posted by Sam Stones on 18/12/2017 06:44:57:

... my three year old PC does not have an RS232 (25 pin) printer socket necessary to accept the dongle......

Sam, I think there may be some clarification needed, as Danny suggested. Most of the answers so far have targeted RS232, but I'd suggest checking before you buy any RS232 kit.

Until the advent of USB, most dongles were fitted to the parallel port of a PC. To save space and cost, instead of fitting the typical Centronics parallel printer connector, PCs used a 25-way D-type connector at the PC end - this physical embodiment is used for both serial (RS232 etc.) and parallel communications - so the fact it is a 25-pin device does not mean it is RS232.

Whereas, as has been said above, you can get 9-25 pin adapters and USB to RS232 converters, I suspect neither of those are what you want.

You are almost certainly in the same boat as many who run PC-based CNC who upgrade their PC. If it is a parallel-port device, you may get away with a USB to parallel port converter, but I would suggest you need to identify one which is known to work with that particular dongle before you buy one. Much better, if you have desktop PC, is to buy a parallel port card to go into the PC.

(and don't worry about criticism for using an old dongle technology - although most of my software that needs dongles is USB based, I do have several old applications I use from time-to-time which use parallel port dongles which I could not justify the cost of upgrading!).


Edited By Dave Martin on 18/12/2017 10:19:33

Thread: PCB CNC
10/12/2017 12:11:17

Bravo Joe - great kit and well explained. Can I just ask - do you ever do double-sided boards on this engraver, and if so, how do you register them and what registration accuracy do you get?


Thread: Small cable connecting
03/12/2017 14:01:46
Posted by SillyOldDuffer on 03/12/2017 13:53:48:

I call this a Post Office Splice and I think it may be what Clive calls a Staggered Joint in his post......

Dave (S.O.D.)

I'm pretty sure when Clive mentioned staggering the joints, what he was referring to is if there are multiple distinct cables, and hence multiple joints, staggering them so the final 'bundle' isn't as fat:


Dave (IOM)

03/12/2017 08:10:14

Rod, just a little caution - I believe those Telecom type connectors are intended for use with solid single-core copper wire, rather than the stranded one would normally find on motors and machine wiring.


Thread: Unidentified Oscillating Engine, possibly marine
08/11/2017 10:05:49


I don't know much about engines, but that looks to me like it may have been designed to run machinery from a belt around the flywheel/pulley.


Thread: Calipers - Dial v digital
26/10/2017 12:45:15
Posted by Martin Kyte on 26/10/2017 09:10:51:

One obvious advantage of digital is the ability to set the zero wherever you require. ....

Also useful if you can't see the display and need to move the jaws to get the caliper out - I've only had to do this a couple of times but very useful. Had to take a measurement in a blind spot so when calipers were 'on' the spot, press the zero button; you can then move the jaws as much as you like. When the caliper is out in a readable location, close the jaws together and the display will show the measurement, albeit with a leading minus sign. Just don't forget to re-zero properly before using again!


Thread: In praise of angle grinders
04/10/2017 09:10:12
Posted by Ady1 on 04/10/2017 07:56:31:

....... Full face helmet and glasses so you can see everything thats going on.......

Would just comment that whilst I do buy some kit/consumables from cost-effective online sources, and those such as that link will be OK for, say, flying dust; I do believe that PPE such as safety visors/glasses are best bought - and worth the small premium - from reputable vendors who can be trusted to supply goods manufactured to safety standards.


Thread: How strong are threads in 3D prints?
24/09/2017 12:44:10
Posted by Neil Wyatt on 24/09/2017 09:08:37:

.......The test rig was basically a 300mm bar with a 6mm hole 25mm from one end so the ratio of forces was 12:1, the block was held in a vice with another bar across the vice to provide a fulcrum level so the bar was pretty much level. I used a spring balance.

I did other experiments with blocks under the vice jaws (not clamped) and 'hook' made from bar so the spring balance could pull up, but the maximum force that way was 75kgf.....

Neil, I would wonder how much compression of the test sample from the vice would affect things - would be intrigued if repeated with just a pair of bars with, say, 7mm holes - so the only force on the block was on its top surface?

24/09/2017 07:49:39

Interesting, thank you Neil. How was the block held - was it, say, below a plate with an M6 clearance hole in it - or was it in a vice? How did you get axial-only pull? Could you post an image of your test rig please?


Thread: Conect 121 lathe
04/09/2017 13:44:52
Posted by Mani Matharu on 04/09/2017 00:11:17:

.....I have an old connect 121 lathe .... Their is very little information off this machine on the net ,,,,,


I can't help with specifics, but I think it is spelt Conect with one 'n' - so if you search for "Conect 121" with that spelling you may unearth more useful information - a quick search on Google listed a number of conversion threads.


Thread: Raw black rubber
01/09/2017 14:00:21


Before you go to any work or expense, especially if this is something you're planning to sell, would suggest you ascertain the hardness of the parts you're trying to replicate (usually measured in Shore, but important to know which scale it is measured - commonly type A or D, but also type O and others - a tyre might be 70 on Shore A, but 70 on Shore D is a hard material like a plastic safety helmet). Once you know your target Shore then you can source materials, and check your end product matches the original.

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