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DRO,s fo Mini Lathes.

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Bernard Owen19/05/2011 15:56:59
13 forum posts
Hi, I have a 7x14 Chinese mini lathe sold by SPG in Hinckley, it is identical to the Clarke Conquest lathe, I want to fit DRO's to the slides and have seen them in Arc Euro Trades catalogue but have been told they won't fit my lathe although the slides look the same as the Seig C3 lathe, I have read David Fenners book on the mini lathe and there is a chapter in there about fitting these DRO's and it doesn't say anything about them only fitting certain lathes, could somebody clarify this situation for me.
Thanks.
Gray6219/05/2011 16:29:33
1058 forum posts
16 photos
Hi,
I had a DRO kit for the mini lathe which was purchased from . I retrofitted it to another chinese lathe although this did require manufacture of new leadscrews.
What is the TPI of your leadscrews, I seem to recall the kit requires a 20tpi leadscrew.
That said, If it is the same kit, then I would not recommend it. It uses rotary encoders which are directly linked to the leadscrew and as such provide no compensation for backlash, in fact, I removed the kit as it was useless as a DRO and replaced it with proper linear encoders and an external readout.
From personal experience, I would not waste money on this type of 'DRO'

jomac20/05/2011 10:15:06
113 forum posts

Hi, if you look on e/bay, you might be lucky, like me, I brought a 600mm long linear scale with seperate readout for A$37, I was the only bidder!!!!! It is for the Z axis on my small mill, it works very well. I also brought 2, 300mm long digital venier scales, which were cheap, although they have sockets I cannot find or know how to fit seperate read outs. So when I get time I will fit the vernier scales for the X/Y axis on the mill table, It is not too much of a problem to lean over to read them.

You have to be lucky, so keep trying.

John Holloway.

Pat20/05/2011 11:15:06
94 forum posts
1 photos
Hi Bernard
 
The Arc Euro Trades are for the Seig mini lathe. However Seig are not the only factory making bench top machines to the same generic specification. This means that there are differences that are much more significant than the paint colors and badges. You will need to identify the manufacturer of your lathe and there are some clues on this web site http://www.mini-lathe.com/Mini_lathe/versions/versions.htm#Versions
I have a Red Bull mini mill undergoing CNC conversion and there are some significant differences in the detail on this mill compared to the Seig X2. I also suggest you compare your printed paper manual with that of the Seig C3 to see if the exploded parts drawings are the same.
 
A better solution is to fit linear DRO's to each slide and a web search will turn up details of how others have enhanced their lathes this way. A cheap alternative is to fit tool maker's buttons to the slide and a fixed reference point for each slide and use a micrometer or digital caliper to measure the movement - a long reach DTI would achieve a similar result assuming that you are only interested on how far you have moved the cutting tool - but remember that the tool must be moved half the distance required to reduce the diameter of the work.
 
I question why you would want to add any sort of DRO that counts the fractional movement of the lead screw and not the movement of the tool tip relative to the machine bed / work as pointed out by CoalBurner. The simple lead screw mechanics used on these lathes means that there is backlash and the methods for adjusting this to be a minimum will not allow it to be eliminated. Any time served machinist will bring the tool to the work always from the same direction making any backlash that remains unimportant. When getting near to size look at the advance on the lead-screw index to gauge how much is actually being removed per division on the scale. A simple bit of arithmetic (source of error so care is needed here!) allows the correct advance to leave a light finishing cut to bring the diameter in on dimension.
 
Good luck - Regards - Pat
 
PS Don't forget the cheap caliper type DROs are not water proof which might be important if you are going to use suds or have a workshop where damp is a problem.  
 
 

Edited By Pat on 20/05/2011 11:17:14

blowlamp20/05/2011 14:07:10
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1613 forum posts
105 photos
Whilst not as elegant as a more expensive setup, I'm finding (the one) I have fitted to the cross slide of my Clarke CL300 lathe to be quite useful and accurate. I haven't fitted a DRO to the top slide because of it's bulk.
 
If you forget about trying to use them in the way you would a 'professional' DRO and think of them simply as 'digital dials', i.e. allow for backlash, then they make some sense. Don't forget they work in imperial and metric too and are switchable at any time.
 
Martin.
John Stevenson20/05/2011 15:49:32
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Moderator
5068 forum posts
3 photos
First of all they are not DRO's, they are DIGITAL DIALS.
 
True they do not take out the backlash as they work on the screws and not the slides, but neither do normal dials. You have to make sure you are always working in one direction, something trainer turners always do..
Where these score is you can switch imperial for metric at the touch of a button, zero anywhere at will but the best advantage is you don't have to count turns and are less liable to making a mistake by taking too much off.
 
Are they better than dials? Yes they are but they are not as good as decent DRO's.
 
The sooner they get accepted as DIGITAL DIALS and not DRO's the less bitching there will be about them.
 
John S.
confused.eng20/05/2011 20:54:47
19 forum posts
2 photos
My brother got these dials for his C3 super.
They are a bit picky about which batteries are used with them - don't use cheap 'equivalents'.
They're ok as a guide but for anything accurate handheld digital verniers are much better.
They were a bit of a sod to fit to his machine and should be treat as a kit of bits to finish.
Only good thing about them is the ability to switch between metric and imperial at the press of a button - he's metric era, drawings are imperial, bit of square peg round hole.

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