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: source of 600 / 1200 grit 6" diamond grinding (cup) wheels,|
Can't help with a supplier but for the numbering scheme, have a look at page 11 of this PDF
|Thread: What did you do today (2015)|
Bob - I hope you get to see the "Star of India" moored at the SD Maritime Museum, she's the oldest iron-hulled ship still afloat & in commission. Some of her history here from the BBC on the 150th anniversary of her launching in 1863, as the "Euterpe". She was built in Ramsey, here on the Isle of Man - and my great-Grandfather was the chief shipwright!
Edited By Dave Martin on 17/06/2015 08:49:48
|Thread: Anti Vibration Mount (camera - motorbike)|
Not sure those basic gyro-stabilised mounts will help. They can damp relatively low frequency variations in yaw, pitch & roll caused by change in the vehicle's attitude - but (unless extremely sophisticated) are unlikely to cope with engine and road roughness vibration.
|Thread: A New Dividing Plate for my Dividing Head|
By'eck - if that's the size of your tea strainer John, what size HobNobs are you on now?
|Thread: I'm Stuck|
I don't know if there's suitable access on your mill quill - but can you get a morse taper ejector in?
Andrew, can't help directly with the overload trip - but as Neil says it sounds like it may be a mismatch. Concerning the motor (over)heating, one aspect you need to beware of when using a variable-frequency inverter is not-only over-speed but also, if you run it much lower RPM than it would at normal mains frequency, if it has a shaft-mounted fan that may now be running too slow to cool the motor properly and you may have to arrange separate forced ventilation that's not shaft-speed dependent.
|Thread: Difficulty in obtaining small machnined bolts|
If metric was acceptable, have a look at Conrad Electronics - I've bought their hex-headed NP brass to use as battery contacts in the past.
|Thread: nuts hex bolts and other|
You might also find what you need, in small quantities, from Conrad **LINK** - although I'm not sure if they do stainless. I've bought various nickel-plated brass from them in small quantities in the past, in the sizes you mention.
Edited By Dave Martin on 11/10/2013 10:47:09
you might just be able to - but I would strongly advise against it.
Firstly, as well as the lens, you would need to remove any ferrous or other non-aluminium components (I suspect the arbor is steel, plus any ferrous fasteners etc.).
Secondly, with the assembled structure there will be significantly higher risk of carry-over. The anodising process traverses a number of process tanks, and it is absolutely essential that the item is purged off one chemical before it enters the next tank. This is often done by a combination of dipping in / spraying with pure water (reverse osmosis / de-ionised or distilled etc.). Carry-over of chemical from one tank to the next can, in extreme cases, "poison" the following tank, but far more likely is an inferior finish. A little acid carried over into the bulk of the dye tank and affecting the bulk pH will have a slight impact on the dye's performance; far more worrying are small localised amounts. If the workpiece isn't thoughly purged of acid, and a little seeps-out during the dying, you can get symptoms like white whisps or streaks or spots.
Thirdly, it would also be harder to guarantee the readiness and that all the wetted surface area would pass the water break test.
Fourthly, if there are, say, any small aluminium retaining rings or collars, there is a possibility that during the anodising run, if they aren't individually racked then they may loose contact and that component wont anodise properly.
For all the above reasons, when we have camera housings, composite lens mounts etc. to anodise they're always racked as individual items.
Anodising isn't really anything to be scared of if you take your time and common sense precautions.
However, if you take it fast & loose then you can spoil things - e.g. inadequate cleaning resulting in un-anodised patches; or excessive etching beforehand giving a matt surface; or anodising too cold and build up a hard layer that won't take dye; or anodising too warm so you get dissolution and a chalky finish; or touching the item part-way through and getting fingerprints; etc. etc.
I think you're right to be scared of, say, the battery-charger/"let her rip" approach which may give variable/dis-appointing results.
BUT if the item is well made, properly prepared and anodised carefully the impact on the dimensions will be minimal and I really doubt you'll have significant issues.
Edited By Dave Martin on 12/12/2012 14:43:13
Anodising does minutely change the dimensions - but depending on your items, you may well not notice them. Anodising is a surface-conversion process - you are converting the surface of the metal into a honeycomb matrix which you can then, if desired, fill with dye and then seal the surface to keep the colour in. There are some notes here which give some background on the process.
Using type II anodising, for a light colour (blue, red, green) you typically need about 0.5 thou total layer thickness; to pack in enough black you need nearer 1.0 thou total thickness. When you're building the ano layer, the very surface is both consumed & converted - its about 50/50 (its actually nearer 60:40 but I can't remember which way!). So, if you're going to colour anodise with a 0.5 thou layer, the item will grow by 0.25 thou for each layer - i.e. 0.5 thou on the diameter.
There is no easy way of masking that doesn't carry risks; and you need to be able to flush out nooks & crannies such as threads between process tanks, so normally threads are left exposed. You will see multi-coloured anodising, or items with some coloured and some left natural - but in these case usually the whole item has been anodised and it has been masked or bleached when it is dyed.
You also asked about the predictability of the coating thickness. Like many engineering processes, if you keep the environment and process constant you can get remarkably consistent results. Using the Constant Current / low current density method, with temperature controlled tanks, we get pretty consistent results (within 0.1 thou or better). Spot checks with our Elcometer show, within the meter's resolution, less than 10% variation in thickness and often better - and the colours match between runs which is our other major criteria.
Depending on how you've cut your threads, you may also find the crests shed their coating and revert to near as small as before coating. Anodising builds a matrix at right angles to the surface, and doesn't take kindly to absolutely acute edges (imagine trying to bend a honeycomb from a beehive around a 90 degree corner). For successful anodising edges need to be 'broken' - radius can be as little as, say, 0.2mm. If you've cut your threads with a full-profile tool, it should be OK; but if the crests have been left sharp they may shed the ano.
Edited By Dave Martin on 11/12/2012 13:38:51
Edited By Dave Martin on 11/12/2012 13:41:09
|Thread: Wanted : source of black M2 countersunk x-head screws|
Hoping someone may be able to point me to a supplier (preferrably in Britain).
|Thread: Help about lagging|
Haven't got a landline phone number for them, I just ordered off their web site. You might get the number from directory enquiries, the address from the web site is
53 Ennerdale close
but a quick google gave a mobile 07958-615187
well - they start with insulation bricks at 29p each ....
cheers / Dave
Edited By Dave Martin on 20/12/2011 15:46:28
Not certain if its suitable for your application, but you can get castable insulation in various grades & densities, such as castable vermiculite, rated to 1050 degrees C, at GBP 35 for 1/2 cwt from Kiln linings
Edited By Dave Martin on 20/12/2011 13:34:23
|Thread: Cleaning ER collets|
|If there's "gunge" in there, try dropping them in an ultrasonic cleaner (just make sure to dry them out properly afterwards though, possibly in the bottom oven on a low heat!)|
|Thread: Milling from a sheet|
Do you think that cafe make's its own lasagne?
Edited By Dave Martin on 12/11/2011 18:06:21
Edited By Dave Martin on 12/11/2011 18:06:57
|Thread: Mill Gearbox Lubrication and cutting oil|
I wonder if there is a confusion over the purpose for the oil.
The reason that I ask is that "68" is very familiar - but not for gears!
I use Mobil Vactra no. 2, which is rated at 68 - but that is the slideway lube - not for transmission.
|Thread: How do I replace the gaslift cartidge in my chair..|
I cannot give you any specific details - but I can say "with great care" !
Some years ago, a colleague had an accident with a gas-lift chair.
He was a great talker, and also renowned for leaning back in his office chair. One day there was a bang from his corner of the office, and we thought he had just leant back too far and toppled over. However, there wa a long silence, so we went to look, fearing he might have knocked himself out falling backwards.
We found him just sat in his chair - but face absolutely white, and saying not a word. He then pointed at the seat of the chair, and then at the ceiling. There was a small rip in the chair, and there, poking out of the ceiling, was a metal rod - the piston rod had let go and shot up through the seat between his legs (luckily he was sitting well back!) and had gone up to, and embedded itself in the ceiling. He did speak again later that morning, and thankfully without too high-pitched a voice.
|Thread: Veteran car models|
It may be worth talking to The Engineer's Emporium who list a De Dion 1903 engine kit
(no connection, just came across their site whilst folowing a link in another thread on this site this morning!)
Edited By Dave Martin on 02/10/2010 10:01:27
From a quick look/read here, areas I would definitely look at are (a) anodising electrolyte make up and control, (b) ano tank temperature control, (c) current density & control, (d) electrical contact, and (e) using proper dyes.
You may find it worth looking at some notes on anodising I posted elsewhere
Dyes - there are some who swear by clothing dyes and many more who swear at them! (especially their un-reliability) You will find a small investment in proper anodising dye takes a major unreliability away. You have to remember you're trying to get the dye molecules down into the honeycomb matrix - so if either (i) the matrix is too fine (ano'ed at too cool a tempeature) or (ii) you have dye moleules that are too big, you won't get much/any dye in there.
Edited By Dave Martin on 04/05/2010 17:03:09
|Thread: Denford Senior 3C Z quill servo?|
Thanks everybody so far
Mark - thanks for the advice but am certain we've got a faulty motor. Have disconnected all of the CNC side and just run it off a lab DC supply and it still jumps (it runs OK for most of the revolution, stops momentarily, and then jumps forward). When driven via the built-in ASR Servotron DC servo amplifier/drive, but with +/- control voltage supplied from a manual pot, the jump is faster as the drive, via the tachogenerator, recognises the motor has 'stalled' and briefly increases the motor power to try to un-stall it and as a result it 'leaps' over the dead spot. With the servo amp driven as intended off the Heidenhain TNC, the situation is far worse as the encoder is then in the loop and the TNC drives it even harder and we end up with an horrendous oscillation as it transits the 'bad spot'.
Unfortunately the other axis motors are much bigger, and there's no chance of swapping-in a borrowed unit - we don't even have an 'ordinary' motor rewinder here - its one of the very rare downsides of living on a rock in the middle of the Irish Sea ! I'm sure its not going to be a Denford or Senior specific servomotor, but it makes it a lot easier to replace or get it rewound properly if I could find the manufacturer's details.
Bob - thanks for the links. Have already aired the subject on the Denford bulletin board without success; and thanks for the link to MYCNCUK - and whilst that thread was about the Starmill on steppers, will also ask there
John (and David) thanks for the feedback. Firstly, apologies if the machine's data plate looked like it was for the Z servo! - the offending servo is completely devoid of any labels at all. Have attached some more general photos below of the machine and the head. Ballscrew is static and the ballnut is driven 2:1 from the motor. Because of the proximity of the ballscrew to the head casting, and I guess desire to limit the overall height, the encoder is also driven off another timing belt.
Whilst the XY travels are great, the quill only has limited travel, so if the knee had been built with a ballscrew, I would have jumped now to use the knee as the Z - but as it only has an acme screw, I'm wary of wearing that out, and will persevere with the quill for now.
In some ways, I think the quill Z might be more of a candidate for a stepper, rather than a servo (lower speeds, more holding than moving). I do have a spare G203V from my small Mach3-driven machine - but in this case I really want to keep the TNC control - so I would need to drive the Gecko off a +/- 10v rather than step/dir ....
If I can't source a new motor, or change to stepper, then I'll be very glad of your help with a rewinder John - its so much nicer to entrust to soemone with a known track.
cheers / Dave
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