The Shop > Electronics & IC Programing
DRO questions
NickG:
The problem I have with this is, most of the stuff we do requires accuracy of a thou or so. Therefore if chinese scales still mean I need to double check everything with manual measuring tools, what's the point in spending a couple of hundred quid kitting the machine out with them? I've managed thus far with manual dials and measuring equipment so what advantage will chinese scales give me other than agro replacing batteries, swarf etc getting into them.
If you're buying chinesey ones then glass scales, you're spending even more money so why not wait until you can afford the proper ones? That's what I'm doing.
Nick
kwackers:
Depends what you do with your scales...
For example - co-ordinate drilling. The tolerance of most bolt holes means a thou is neither here nor there. Chinese scales (at least the one's I've used) have decent repeatability. They suffer from thermal expansion and contraction as do glass scales (and your machine) so close fitting parts need to be machined consecutively - especially if like me you share your space with a kiln!
In practice even where accuracy is required you can quickly machine close to size with Chinese scales, for 90% of stuff though I found the accuracy fine.
You've also got to bear in mind if you're not using coolant (I don't usually) then the act of machining a part will change it's size considerably. I'm sure we've all been there, make a part that's a good fit then when it's cooled it just 'drops' through!
But yeah, if you're intending to replace the Chinky scales in a relatively short time scale there's no point.
I had Chinese scales for 5 years fitted to a fairly rubbish Chinese lathe, whilst I had that lathe I wouldn't have considered spending it's value on glass scales, in terms of accuracy they wouldn't have helped...
When I got round to upgrading my machinery I felt both it and me had progressed to a point whereby it was worth buying and fitting higher quality scales.
picclock:
As another take on chinese scale accuracy, the tolerance of +/- 1 thou is over the length of the scale. The resolution of the scales is 0.5 thou or 0.01mm. This means that over a short distance after the scale has been zero'ed the accuracy is far better than the +/- 1 thou, and the repeatability also.
On my mill the measurement of a given point changes by 1 thou just from when its cold in the morning to when the workshop has warmed up. As this seems to occur repeatedly and consistently, I surmise that this is the machine table changing size with the temperature change.
So the chinese scales are cheap, but I think they are very accurate for the price you pay. Once fitted, no one is going to go back to counting turns on a handle with its associated backlash issues.
I am considering fitting the scales with a full length flexible rubber(?) cover or a tube with a slot in it and using a remote readout - but so far its just one of those jobs on the tuit list.
picclock
z3t4:
--- Quote from: j45on on February 19, 2011, 04:23:11 PM ---
Hi z3t4 John
I would love to see some pictures of your scales.
Did you get your "Wixey tablesaw DRO tape" from the UK ?
--- End quote ---
Hi Jason
The tape was left over from adding their digital saw fence thingy to my tablesaw. I had been impressed by the DRO 350 and it seemed to me that an experiment using this tape and the Virtual Village scale heads would be worth a punt. At a fiver each it would be rude not to. I got the heads back in May 2009, at which time they cost £3.77 each. The Chinese seem to have upped their prices for geek-food since. The tape was free but I subsequently got some more from Allendale. I think it was very cheap (2 metres for £~20, ISTR).
The issues that JohnS has mentioned were very much in evidence for the DRO 350 but part of the motivation for the DRO 550 was to address them. It is possible to read most scales but Spherosyn, Mitutoyo and some of the newer Chinese ones are, er, resistant. It may be that the firmware will be developed to read more protocols. Certainly there are some very bright people on the Yahoo group. I have not found jitter or wildly erratic display to be a problem with the new DRO.
For my part, I just love messing with this stuff. If I were depending on it to buy Jaffa cakes no doubt I would get a Spherosyn properly fitted. But then I would be working to gnat's bollock accuracy, and I don't have the skill nor the kit to do that. I am (honestly) in awe of people like JohnS and Bogs, who not only do have that skill but are willing to share it with those of us who want to learn.
This is a pic of the gutted head with an unmolested one in the background (NB anti-jitter capacitors):
This is a closer pic:
This is the tape and the extrusion, waiting to be fixed:
This is it working:
HTH,
John
edited for typos
John Hill:
Thanks John S. and John Bogstandard.
OK, so the accuracy of the job depends on how accurate one is in measuring the starting diameter and if you are careful there the final size will be accurate without further measuring? I can see that would be a great advantage but not so much if it is still necessary to make a final check with the micrometer. :coffee:
I have a simple system using Chinese scales operated by flexible cables which is great for avoiding gross errors but I still have to 'sneak up' on the final diameter.
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