Author Topic: DRO  (Read 2895 times)

Offline crankshafter

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DRO
« on: June 18, 2015, 10:49:24 PM »
I'v got to the point where I'm ready to order a DRO for my lathe. The lathe is a eastern 12-36". This is maybee a silly question :slap: but how long scales do I have to order??

Best reg.
CS
"I cut it twice, and it's still to short"!!??">#%

Offline CHP

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Re: DRO
« Reply #1 on: June 18, 2015, 11:22:29 PM »
6 inch for the cross slide, and I used a 30 on the Z
I have a 12x36 also

and love it  :cartwheel: :cartwheel:
12x36 lathe,Seig7x10 lathe, Taig lathe
9x29 Mill, Emco 55 CNC mill.......

Offline Brian Rupnow

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Re: DRO
« Reply #2 on: June 18, 2015, 11:26:05 PM »
If you go to the dropros.com website, they give a very detailed expalanation of how to calculate what scale length you will need.---Brian

Offline Jo

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Re: DRO
« Reply #3 on: June 19, 2015, 07:52:50 AM »
CS it is not as simple as it first seems  :hellno:

As a minimum each scale needs to provide the necessary movement/measurement of the axis on the machine. Sometimes you will find it easier to mount the scale if you buy a longer scale. So before you order them have a think about where you are going to mount the brackets to support the scales and if you would prefer to mount the measurement head somewhere specific and if the cable run might get in the way  ;)

For instance on Sexy  :Love: I have brought him a 220mm long scale for the X axis to bolt on under the table mount but the table only has 150mm of movement. I will be getting round to mount his DRO on him shortly  :whoohoo:

Jo

P.S. are you looking for a two channel or three channel setup? If the feed on your saddle is very coarse then putting an extra channel on the top slide can be useful, like on my Colchester  :)
 
Usus est optimum magister

Offline Carbuilder

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Re: DRO
« Reply #4 on: June 30, 2015, 01:45:07 AM »
If you get the magnetic scales (bought mine from Dropros), you can cut them down so don't be afraid to get them too long. I put them on my Busybee 3-in1 machine.

Offline Overbuilt and Overkill

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Re: DRO
« Reply #5 on: August 15, 2015, 03:37:09 AM »
An older thread so this might be far too late to help the original poster. But I hope it might help someone else in the future.

Jo is also more than correct about figuring out how and where you'll mount the scales before buying the DRO.

If you want a DRO's scales to measure the machines full travel then you have to allow for whatever distance the scales reader heads cover of each spar or scale. Let's say your carriage will travel that full 36" and your reader heads are 3" long. A 36" long scale will still be too short. If? and you'd have to check with the DRO's dealer to be 100% sure of how and where your exact brand of reader head gets there signal. So if your reader heads get there measurement signal from the center of each head, then you need an additional 1.5" length on each side of the scale to allow the reader head to travel the full distance that the machine does. And if it were me, I sure wouldn't try to have anything quite that tight for length. The last thing you want to do is be even .050" too short. Those expensive reader heads and the very delicate glass scales if your DRO has them instead of the magnetic type just don't like those interference fits. Better to add at least 1" or 1/2" to each end to be safe. If you are dealing with a good company who do know there own product? Then yes you should be able to just give them the travel measurements for each axis and they will automatically add in the extra length you'll need. If your ordering directly from China as some do today? I'd want to be a little more sure I was getting a scale that was more than long enough for my machine.

Yes for most of us it probably would be more than rare to use everything the machine has for travel on a lathes carriage. And you could tell yourself that you will remember not to ever go to the machines full travel limits. But it only takes once to forget and you could be looking at a less than welcome repair or replacement bill. And that's if there still making and have any repair parts available 5 or 10 years from now. The only other way to be safe is to attach a mechanical travel limit so it's physically impossible to over travel a scale that's too short. In my opinion a few extra inches on the scale or scales costs so little extra in the overall price of a good DRO that there's really not much point in trying to go too short just to save a few extra bucks or those pounds for the UK members.

Greg 
« Last Edit: August 15, 2015, 03:55:18 AM by Overbuilt and Overkill »

Offline Jo

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Re: DRO
« Reply #6 on: August 15, 2015, 07:26:16 AM »
Greg,

All of the scales I have come across are quoted by their distance they are able to measure, the physical scales are longer than this. For instance I have a spare 170mm scale, it is 280mm long and having just moved the head from one end to the other found it will measure 175mm.

I must get around to fitting that spare DRO on Sexy  ::)

Jo
Usus est optimum magister

Offline Overbuilt and Overkill

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Re: DRO
« Reply #7 on: August 15, 2015, 09:57:00 AM »
Jo,
Hmmm, in Canada the scales are listed as the total length. Or at least the company I bought mine from had them listed as such. The extra as I mentioned had to be added. So it seems I've given some misinformation. If one of the moderators could delete my whole post I think that would be best.

Greg