Author Topic: From the den of the Artful Bodger, a poor man's DRO!  (Read 14914 times)

Offline John Hill

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From the den of the Artful Bodger, a poor man's DRO!
« on: February 20, 2009, 03:38:12 AM »

The poor mans DRO!  Mounted on a 'lecturn' fixed to the back of the lathe carriage.


How the cables are attached to the back of the DROs, it is a slip joint which is necessary as the carriage travel is more than the maximum length of these DROs,  it just hits the end and the cable slips.


How it looks behind the DROs.



One of the cable anchors.



One end of the cross slide cable loops under the lathe bed.


The DROs cost about 50 quid and the cables another 10 or so including the length of stainless fishing trace I had to use for the longer cable.

So how good is it?  Wellll I guess you get what you pay for and this is not a 500 quid DRO set but it is certainly functional and I can wind the carriage back and forth then return to a marked spot and it reads zero. There is a slight backlash which I can probably work on, the cross slide is worse than the carriage travel as far as back lash is concerned  which may be because that cable is spring tensioned, the long cable is tensioned by screw adjuster and has less backlash.  I still need to dress the flexible sections and shorten where I can as I believe the flexible sections are the cause of the backlash, but I am not going to get too obsessive about this.

All in all I am really pleased with the result, it did not cost much and the DROs are well out of the way of coolant etc, plus the steel lecturn gives me a place to places notes and small drawings etc.
From the den of The Artful Bodger

Offline SPiN Racing

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Re: From the den of the Artful Bodger, a poor man's DRO!
« Reply #1 on: February 20, 2009, 04:17:22 AM »
WOW... very inventive way to get the DRO setup taken care of!!

I would imagine once you get used to the slight backlash in the cables.. its easy to be accurate.
SPiN Racing

bogstandard

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Re: From the den of the Artful Bodger, a poor man's DRO!
« Reply #2 on: February 20, 2009, 06:19:48 AM »
John,

Very inventive, but your choice of using bowden cables is the downfall.

No matter what you do, you will never get them to have zero backlash unless it it a perfectly straight setup, and how you have done it, tensioned with some sort of spring. The problem is the running clearance between the cable and the outer sheath, and going around corners, you will always get some flexing of the outer sheath.

The method was used many years ago in the beginnings of DRO's on model engineering equipment, but without the outer cable. It operated similar to a steel tape measure, where the amount of cable pulled out, turned a rotary encoder. It did have the advantage that it could be used with a rotary table as well, as the cable just wrapped around the turny bit on top.

I don't know if anyone actually bought any, as they soon disappeared from the market.

I wish you luck on your efforts to get zero backlash.


John

Kludge

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Re: From the den of the Artful Bodger, a poor man's DRO!
« Reply #3 on: February 20, 2009, 07:39:11 AM »
Bogs, as I was reading your message, the first thing that came to mind was to use hydraulics instead.  A cylinder at each end and a well purged system would do nicely, though it might be a bit upset at any overrun at either end.  Gotta think about that bit.  It could be fun, though.  :)

Best regards,

Kludge

bogstandard

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Re: From the den of the Artful Bodger, a poor man's DRO!
« Reply #4 on: February 20, 2009, 09:49:14 AM »
Absolutely great Kludge, until you have a saddle feed like mine, of 3ft. I wouldn't like to be on the other end of a syringe that long. :lol:

Bogs

Offline John Hill

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Re: From the den of the Artful Bodger, a poor man's DRO!
« Reply #5 on: February 20, 2009, 02:32:40 PM »
Bogs, all understood.  The long cable has less backlash and that one is screw tensioned, the cable is quite tight  but I know what will happen and that is the cable will soon cut the plastic liner of sheath and need more tension.

The cross slide cable has a rather long flexible cable to go under the lathe, I assume this would be better if I used rigid conduit instead of the sheath.

Maybe a 500 quid DRO allows you to do away with the calipers and micrometer?  If not then this is a pretty damned close second place getter with 450 quid to spend on other toys.
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bogstandard

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Re: From the den of the Artful Bodger, a poor man's DRO!
« Reply #6 on: February 20, 2009, 05:08:50 PM »
John,

If you are not into flooding everything with coolant, as I am, you can get away with the type of digital caliper you are using actually mounted onto the machine. In fact for the topslide and tailstock, el cheapo digital calipers can be cut up to do the job. Just make up ali swarf protectors and feed the readout to a remote display head. But again, they are not overly cheap if you have to buy 3 of them.
The cross slide could be done with the type you have now. The saddle is the problem, you should see the size of my read head, it is over 3ft long, thank goodness mine came with the machine.

John

Offline John Hill

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Re: From the den of the Artful Bodger, a poor man's DRO!
« Reply #7 on: February 20, 2009, 07:25:20 PM »
John, it is not that I flood everything with coolant but if I did I am sure that would be the end of directly mounted El Cheapos!

My saddle travel I can only do relative but there is 30cm to play with.

I found a length of small diameter (6mm?) steel tubing on the street today ( ::)) which maybe what I need to improve the cross slide backlash.  Mind you the backlash on the DRO is much less than on the handle scale!
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Offline Divided he ad

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Re: From the den of the Artful Bodger, a poor man's DRO!
« Reply #8 on: February 20, 2009, 11:06:34 PM »
Interesting.... I can honestly say I have never seen anything like this before.

It would never have even occured to me!

There certainly is an art to this bodging   :dremel:  :thumbup:

Any more accurate than the dials has to be better doesn't it?




I certainly like the way your brain works John  :clap:




Ralph.
I know what I know and need to know more!!!

Offline John Hill

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Re: From the den of the Artful Bodger, a poor man's DRO!
« Reply #9 on: February 20, 2009, 11:13:28 PM »
Maybe it is better than even I thought!  I did a little test today, I took a few inches of 22mm mild steel bar the local engineering shop gave me from their junk box.

I faced off one end then took a very light tidy up cut for half its length and when I did I zeroed the DRO,  then I flipped the piece end for end and faced off the other and after moving the tool to the zero position I took a cut from that end. When the two cuts met I could actually see the meeting point but it was so close and I could not feel any difference.
From the den of The Artful Bodger

Kludge

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Re: From the den of the Artful Bodger, a poor man's DRO!
« Reply #10 on: February 21, 2009, 07:27:05 AM »
Absolutely great Kludge, until you have a saddle feed like mine, of 3ft. I wouldn't like to be on the other end of a syringe that long.
Ever have a colonoscopy? :(

Since the largest lathe I can imagine having would be something like a 109 (or something of similar size), the problem is reduced but even that could be an unpleasant experience should something go terribly wrong.  So we make it so nothing can go wrong ... go wrong ... go wrong ...  :D

BEst regards,

Kludge