Author Topic: DRO questions  (Read 41017 times)

Offline Bogstandard

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Re: DRO questions
« Reply #25 on: February 20, 2011, 06:08:07 PM »
Quote
unless your scale is fitted to the tool point there are a myriad of ways in which accuracy can be compromised.

Actually Steve, after using glass scales for the last couple of years, I can even tell when a tip requires replacing to bring me back on line to getting about 5/10ths accuracy.

I worked with vernier scales for a few years, and really struggled to keep my accuracy within a thou or two, they really are sometimes very inaccurate and obstinate. Whereas after using glass scales for so long now, hitting 1 thou accuracy could almost be done without even thinking about it, and that could be hit time after time after the machine has been allowed ten minutes to warm up.

It all depends what you are after, and in my case it was what my customers required. If I couldn't hit 5/10ths or better either way, they weren't interested.
That is all finished with now, but having got used to it, I would never go back to anything less.

With regards to the newer magnetic strip heads. I am under a personal opinion that if you are working with any sort of ferrous materials, especially cast irons and steels, you might be asking for trouble. The size of particles coming off either of these two materials can be absolutely minute, and could be attracted thru even tiny gaps where they could adhere and cause problems. As far as I am concerned, the jury is still out on those, and until they are proved to be unaffected, I would prefer to stick with the slightly longer glass scales.

But if anyone would like to donate a few of the latest Newall scales, I would certainly take them off their hands as a direct replacement for mine.


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Offline John Hill

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Re: DRO questions
« Reply #26 on: February 21, 2011, 03:25:17 AM »
I have not yet progressed to the point where I understand just exactly how DROs can be used for accurate work on a lathe.

Suppose for example I want to turn this bit of rusty steel shaft down to a diameter of 20mm. I mount the bit of steel in the lathe, touch up a suitable tool with my hone and mount it in the tool post.

How would I set the DRO, if I had one to indicate exactly 20mm when I have reduced the diameter to that? :scratch:
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Offline John Stevenson

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Re: DRO questions
« Reply #27 on: February 21, 2011, 03:52:30 AM »
You take a cleanup pass and measure that, then set your DRO to that value.

John S.
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Offline Bogstandard

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Re: DRO questions
« Reply #28 on: February 21, 2011, 04:11:43 AM »
First off John, you would take a light skim off the rusty old bar to get yourself to clean metal. Then take a micrometer reading off the bar.

Depending whether you work in imperial or metric, you press a button on the display to put you into the correct units, then press another button to zero up the display.

Also depending on how you originally set the display up, either amount off the diameter, or like most people and lathes, amount off radius (1mm off radius takes 2mm off the diameter).

You can then do what John S has said, input that figure into the display and cut until your display shows what you want to end up at.

Or do it the way I do, a**e about face.

Subtract the diameter you want to end up at, say 15mm, from the mic measurement, again say 19.5, leaving 4.5mm.

By taking your cutter display into half that figure (2.25mm) in easy stages, once you reach 2.25mm on the display, your bar should be exactly 15mm diameter.

That does sound rather complicated, but in fact, once you get used to it, everything becomes second nature and you can cut down to your 15mm size continually, time after time. In fact if you zero your tool when you reach the correct size, no matter what size bar you put in there, if you cut down until the display shows zero, you will be at 15mm diameter exactly.

There are different ways of doing things with these display boxes, each type having various features you can use, even some that will help you to turn tapers.

Depending on the type of scale that is fitted to the display, governs how accurate and repeatable the cutting action becomes. Using cheap vernier scales you would expect your accuracy to be within 0.002" (0.05mm), whereas with the more expensive glass scales, that figure can become 0.0002" (0.005mm)


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Offline kwackers

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Re: DRO questions
« Reply #29 on: February 21, 2011, 05:12:54 AM »
It all depends what you are after, and in my case it was what my customers required. If I couldn't hit 5/10ths or better either way, they weren't interested.

Hi Bogs, your point above is what I mean. Most of us amateurs don't have customers, we also lack both decent machinery and the nounce to make do with the slightly iffy stuff that abounds.
(I've long observed that a good man can do fine work with poor tools, whilst a poor man will always benefit from good tools).

Fitting glass scales to an amateur machine and suddenly expecting 2/10ths accuracy is bound to lead to disappointment. Many machines don't allow for good placement of the scales meaning racking can be an issue and that's before you come to realise that they're not a substitute for machining skills.

There does seem to be an attitude on here that it's glass scales or nothing and that's simply not true. I survived years with cheap chinese scales and managed just fine. I think rather than be put off because people can't afford a full set of glass scales people should be encouraged to use what they can afford. Chinese scales make a lot of things so much easier even if you have to crane your neck to look at the built in display.
When I changed machines I switched to glass scales and there's no doubt they're an improvement but if I couldn't afford them then I'd have no hesitation using Chinese scales.

Offline NickG

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Re: DRO questions
« Reply #30 on: February 21, 2011, 07:57:47 AM »
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
Location: County Durham (North East England)

Offline kwackers

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Re: DRO questions
« Reply #31 on: February 21, 2011, 08:22:33 AM »
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.

Offline picclock

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Re: DRO questions
« Reply #32 on: February 21, 2011, 10:02:15 AM »
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



 
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Offline z3t4

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Re: DRO questions
« Reply #33 on: February 21, 2011, 01:31:17 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 ?

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
« Last Edit: February 21, 2011, 04:39:50 PM by z3t4 »

Offline John Hill

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Re: DRO questions
« Reply #34 on: February 21, 2011, 01:53:20 PM »
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.
« Last Edit: February 21, 2011, 01:55:08 PM by John Hill »
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Offline John Stevenson

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Re: DRO questions
« Reply #35 on: February 21, 2011, 04:27:00 PM »
Don't get me wrong I am not knocking the Chinese Digi-callipers, I think they are marvellous and I have about 8 or 10 around the shop.
Every machine in common use 'should' have one but what happens in practice is that the most used machine has six  :scratch:

However once you know the limitations they are easy to work round, I tend to get close with the callipers, then swap to micrometers if needed, things like bearing diameters need to be spot on so it's micrometers to finish.

Tomorrow I have to make 3 long shouldered bolts with three diameters, 25mm, 22mm and a 20mm x 2.5 pitch thread, none of these diameters, lengths etc are critical and I'll use the digi-callipers for everything. No point working to tenths when not necessary, it cost money to do this and it's usually my money so that's a big incentive. :beer:

My complain with the 350 was jittering and because it was on a lathe, the accuracy. I have a Sino readout now and it works well but I still don't rely on it all the while, my main lathe a TOS 14 x 40, is now about 10 years old and still deadly accurate on the dials, if I put 0.025mm on it will remove 0.025mm from the diameter. The Sino will follow this the 350 wouldn't.
John Stevenson

Offline BillTodd

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Re: DRO questions
« Reply #36 on: February 22, 2011, 06:24:29 AM »
Quote
The tape was free but I subsequently got some more from Allendale. I think it was very cheap (2 metres for £~20, ISTR).

John that 'tape' is exactly what I've been looking for - still am ;) I can't see it on the Allendale site, do you have a link?

Bill

[edit]

Ah ha found it  ----- out of stock ! :(  :bang:

BTW JohnS I still intend to experiment with an optical mouse or encoder based digital trava-dial, but I'll continue it here, as there'll be less chance of bumping in to an know-all/nothing idiot ;)
« Last Edit: February 22, 2011, 06:33:36 AM by BillTodd »
Bill

Offline j45on

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Re: DRO questions
« Reply #37 on: February 26, 2011, 11:45:19 AM »
Bill
they have the tape/strip here WR7003 Sensor Strip Set third item down

http://www.wixey.com/fence/spareparts/index.html
Jason

Offline John Stevenson

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Re: DRO questions
« Reply #38 on: February 26, 2011, 01:42:12 PM »


BTW JohnS I still intend to experiment with an optical mouse or encoder based digital trava-dial, but I'll continue it here, as there'll be less chance of bumping in to an know-all/nothing idiot ;)

He seems to have disapeared, whatever the forum is running well now about 3 or 4 people are missing.

John S.
John Stevenson

Offline BillTodd

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Re: DRO questions
« Reply #39 on: February 27, 2011, 10:06:33 AM »
Thanks for the link, Jason   :thumbup:
Bill

Offline j45on

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Re: DRO questions
« Reply #40 on: March 02, 2011, 02:32:44 PM »
Got some scales today and I am glad I did not order the 16" as the 12" is 17"s long and will read just over 13"s
Unfortunately I am going to have to send one of the 12" ones back as it looks like a banana  :(

Jason

Offline j45on

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Re: DRO questions
« Reply #41 on: April 17, 2011, 02:43:28 PM »
I built my DRO-550 today which came in the post last week so now I need to pull my finger out and finish adding the scales  :hammer:
I also need some scale cables is the mini din 4 pin connector the same as an s-video lead plug ?
If they are I can buy a long one from ebay and cut it in half and solder the other end to the scales  :zap:

Sorry cr*ppy camera phone picture again
This picture makes the led's look washed out,I also need to make a mounting arm :dremel:
Jason

Offline Bluechip

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Re: DRO questions
« Reply #42 on: April 17, 2011, 05:28:37 PM »
Jason

4-way mini-din ???


Piccy herewith:

http://uk.farnell.com/pro-signal/av00948/lead-4pin-mini-din-plg-plg-3m/dp/3712394

Fairly common item

Dave BC



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Offline j45on

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Re: DRO questions
« Reply #43 on: April 17, 2011, 05:48:04 PM »
Yes thats the one
I have just bought a s-video lead from ebay to see if it is the same 99p with free postage ,I thought it would be worth a try
looks similar http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=320658616652#ht_3623wt_1032
It will probably be cr*p though
Jason

Offline andyf

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Re: DRO questions
« Reply #44 on: April 17, 2011, 06:13:22 PM »
Condensed quote from the Maplin catalogue:
"Mini-DIN plugs ... available in 4,6 and 8 pin types. The 4-pin is the standard S-VHS connector, the 6-pin is the standard PS/2 keyboard and mouse connector. "

It doesn't say what the 8-pin is used for.

You were wise to buy a made-up lead. It's bad enough soldering to a full-size DIN plug or socket; mini-DINS must be a real pain.

Andy
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I've cut the end off it twice, but it's still too short

Offline j45on

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Re: DRO questions
« Reply #45 on: April 17, 2011, 06:21:42 PM »
Thanks Andy

Thought they looked the same and that confirms it  :thumbup:
I just hope the s-video lead has four core cable and not a pair of tiny coax cables.
Jason

Offline j45on

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Re: DRO questions
« Reply #46 on: April 21, 2011, 03:20:38 PM »
I got my 99p s-video cable today and it is a perfect fit and has four separate wires but it is very thick and inflexible so I think I will have to buy some plugs and make my own.  :zap:

I am also struggling to find out what capacitor/s to solder into the scale in place of the battery does anybody know ?
Jason

tumutbound

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Re: DRO questions
« Reply #47 on: April 21, 2011, 09:53:38 PM »
The value of the capacitor(s) is not critical.
According to the Shumatech site, anything up to 330uF electrolytic with a .01uF ceramic in parallel.

I used a 100uF as it was the largest I could get in an SMD package.

Offline j45on

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Re: DRO questions
« Reply #48 on: April 22, 2011, 07:16:11 AM »
Cheers Tumutbound  :beer:
Kenneth  :thumbup: if I wanted to build a cable from scratch what would you recommend ?

I added some green filter today I was not happy with the colour it was a bit yellow under my shop lights
I'm happy now but I had to buy a roll just to get the bit I needed  :palm:
So I have some spare if anybody needs a bit for their dro  :thumbup:

Before


After
Jason

Offline andyf

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Re: DRO questions
« Reply #49 on: April 22, 2011, 09:47:32 AM »
I got my 99p s-video cable today and it is a perfect fit and has four separate wires but it is very thick and inflexible so I think I will have to buy some plugs and make my own.  :zap:


Not that I want to discourage you, but in MEW issue 111 (Dec 05/Jan 06) there's Part 1 of a series about using chinese calipers and the Shumatech 350 readout.

The author said: "I found my 4 pin DIN plugs and sockets on the back of the DRO a nightmare to solder up. [They] just have solid pins to solder to. A type with solder buckets would have been easier with less possibility of solder bridges."

Good luck!

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short