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Is a dro on a lathe really that useful?

Jason Harris

Aluminum
Joined
Sep 4, 2005
Location
Auckland, New Zealand
Hi everyone, as you can see from my last post I am getting ready for a lathe. I wanted the dro's as I also have them on my mill.

Now I can see how usefull they are on the mill but I have a problem with the lathe.

You cant make really fine adjustments with the carrage handwheel so you have to finish off with the compound. Trouble is the dro reader is not attached to the compound for the x axis.

This leads me to think that the dro will get you close but you have to finish off with a dial anyway - so whats the point? I can get myself close without a dro.

How do you guys do it? Is a dro on the lathe really worth it? I dont mid the extra ~$700us to get the dros but it seems like it might not be all that usefull on the x. Is the value really there for the y axis?

Thanks,
Jason
 
get one on the carrige and adapt a digital calliper to the compound

---or bite the bullet and get a 3 scale dro that sums the scales, even figures in the angle of the compound
 
DRO on a lathe or mill, while not essential in a pure sense, is supremely valuable. Get it. You will never regret having it.

Joe
 
Hi dk, I understand the benefit but the pitfall with the 2 axis models I have seen is if you move the compund you have lost your position as far as the dro is concerned.


Now, if you never need to move the compound and can control the hand carrage accurately then its not a problem but I dont think I can accurately come across a millimeter or less without using the compound, there isnt that precision in the lathes that I have looked at.


Once again what that means is that I can get close with the dro but have to use a dial, or caliper as suggested, to finish off with the compound.

Thanks,
Jason
 
The real accuracy I'd be looking for in a lathe DRO is on the Z (spindle) axis.

Suppose you want to machine a step .344" away from the end of a shaft....

Producing accurate diameters on the lathe isn't that big of a deal, it's producing accurate lengths.

Granted there are mechanical work-arounds like Trav-a-Dials and dial indicators & indexing length stops, but a DRO will tell you quickly and exactly where your tool is at on the complete length of the bed.

-Matt
 
"I dont think I can accurately come across a millimeter or less without using the compound"

*This* is a serious problem. A mm being roughly .040".

You should be able to turn to .0005" by splitting the graduated lines on the crossfeed dial.

Not to bust your balls but perhaps a bit more practice in manual mode is in order....

-Matt
 
dsergison, I just had a look at the three axis dro's. I didn't know that some of them have the ability to sum up two axis as you suggested.

This seems to be the best way - to put a scale on the coarse feed and a scale on the fine feed and let the computer work it out. I think I am off to price it up now


Thanks,
Jason
 
Hi Matt, I know I need more practice


I can easily achieve it on the fine coarse with the compound but the main hand carrage can get sticky and I worry about applying just a little too much pressure and overshooting the mark.

Perhaps it was still full of chinese grease, I dunno.

Thanks,
Jason
 
Matt, just read your post again. Crossfeed is ok - thats not a problem.

I was just concerned that the x axis dro is attached to the main carrage which is only controlled by the main hand carrage wheel which is not the most accurate wheel on the lathe.

Jason
 
Yep, Jason, I read the posts again, I think we were talking about two different movements. Never mind what I said...


The beauty of the DRO is you can tweak and tweak until you get it just right. I think you would be surprised how well you can do once there's a "feedback" mechanism.

One question for Dan is how does the compound DRO scale convert to X and Z? I would think that a rotational encoder would be needed to assess the angle....kind of like polar coordinates...

-Matt
 
Jason, I've had the same concern before final mounting of a DRO on my lathe ... coarseness of the carriage handwheel.

I was reading an old South Bend catalog last night and what they offered for their 10" (and up??) lathes was a planetary geared carriage handwheel. You switch between standard and geared-down longitudinal feed. I think something like may be worth pursuing for my applications.

Just another option which might help long term with your concern.

Another option is to keep the cross slide parallel to the bed. Use the carriage handwheel and DRO until the last 0.010" or some number that's easy to remember and factor in. Then, use the cross slide handwheel to finish to size with fine motor / brain control ;)

Den
 
dsergison, I have seen DRO so can take the input from two scales operating on parallel axis, such as the knee and spindle of a Bridgeport, and report the relative distance between the two. I have never heard of one that could take the input of one axis operating at an angle to two other axis and keep track of their total relationship. I know that it could theoretically be done, you just have to enter the angle relative to the axis, but I have never actually seen that done. Can you buy such a DRO? If so, please tell me which brands offer that feature, and which models.

Thank you
Ed
 
Fortunately for me, our Summit lathes were equipped with a dial on the carriage handwheel with .005" graduations and 1" per revolution travel. Although not precise for positioning, it was better than nothing. A long Z axis scale costs a lot of money, especially if using Sony brand.

So we have Sony scales on the cross slides only. This certainly helps a lot when making multi-stepped shafts, but I believe the real strength of the DRO is to program in the tool offsets for all the turning tools and boring bars. Punch a couple of keys after changing the quickchange tools, and you are ready to go......no need to find your place again.

For precision turning (boring motor endbells mostly), a high precision X scale (.00005" radial precision) is not to be scoffed at. When trying to scrape out 2 to 5 tenths, a precise DRO will tell you if you actually succeeded in moving the cross slide or not when you are trying to tweak the tool position. It will also tell you if normal machine vibration is causing the tool to drift to a new position during the cut.

Our biggest lathe is also used for precise bearing bores, without a DRO. So we do split hairs using the regular cross slide dial. The slight bit of wear in the carriage creates a bit of slew which tilts the carriage. We can count on getting about .0004" extra cut if we bore with the tool coming out of the bore, without adjusting the position at all. So we make use of this characteristic when the time is right.

A good portion of taking extremely light finishing cuts is learning to "read the chip" and watch carefully the volume and rate of formation of the chip nest. After a while, you can tell right away if you are getting more than you intended, so you can stop and try again before oversizing the whole surface.
 
Jason,

I spoke to Heidenhain about such a problem of using the carriage wheel for determining lengths. When I told him that I wanted a scale on the Compound the response was "Ah you want a European setup". Unfortunately he could not provide me with examples of how they were mounting the scales on Carriage. I have heard that Heidenhain has a new DRO ND 780 (I made several posts requesting information but no bites or answers to date). The ND 780 apparently will be priced similar to the 750 but will have memory for 9 tools. It is a three axis DRO can sum two of the axes or show them independently.

Raymond
 
Pricing it up it looks like it would cost me an extra $1400USD to upgrade to a 3 axis dro which will sum up 2 axis.

This would solve the problem but its expensive.. I would be keen to hear from p[eople about wha they do actually do eg a fancy dro like above or use a dial or stick on a cheap digital caliper to the cross slide.

Thanks,
Jason
 
Jason,

Among the mechanical work-arounds that Matt mentions, I think that a cheap and effective one is to put a 1-inch plunger style indicator onto a "Might Mag" and stick it onto the ways in front of the headstock, just to the left of the carriage.

For under $20, you can buy one of these sorts of setups from Enco: http://www.use-enco.com/CGI/INPDFF?PMPAGE=198 (look on the middle right hand side of the page, item number 625-0455).

I don't use my home lathe nearly as much as I use my mill, and I don't miss the lack of DRO on it. But I guess it depends on how much and what sort of work you do. Personally, I would much rather spend $700 on other lathe tooling (chucks, steady or follow rest, toolholders, etc.) instead of a DRO. I don't know what the equivalent to Enco exists in NZ (here in the USA, we have Home Depots instead of Placemakers), but you can probably find something for under $50 NZ.

-Jon
 
sometimes when you think youve seen it all....

consider getting a setup that has multiple tool offsets or at the very least absolute and incremental offsets.
invest in a notepad and some pencils to write down relevent numbers.
get the finest resolution you can.
take all the backlash out of the compound or lock it with a toolmakers clamp.
turn the headlights on...jim
 








 
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