Scales and DROs

[TerrydParticipant @terryd72465]

Hi all,

During a long and varied career I have always been involved with manual machines or small cnc. I have never used a manual machine with a DRO and scales and know little about them. I am considering equipping my milling machine and lathe with scales and DRO.

My question is, can both machines share a DRO, or do I need a dedicated one for each?

Best regards

Terry

[TerrydParticipant @terryd72465]

[JasonBModerator @jasonb]

Its not that easy to just flick a switch and change the same console from milling to lathe mode, you end up having to change directions of scales and alter a few other perameters.

I've not really found the need for them on the lathe but would not be without them on the mill. If you can afford it then don't bother with the calliper type scales I found them to be too unreliable, they are in the back of a cupboard now gathering dust.

J

[Another JohnSParticipant @anotherjohns]

Terry;

On my (inch based) Kerry lathe, I have 2 0-25mm travel dial test indicators. (you know the things with the plunger on one end)

I have some strong magnets taken out of 5.25" hard drives, and in essence (via aluminum bits and blobs) attach these to the compound rest and cross slide.

I keep thinking "one of these decades I'll DRO the lathe" but to tell you the truth, the 0-25mm dials are probably more convenient as they are right there, and analogue (much easier to read, like analog watches compared to digital)

Certainly, sometimes swarf sticks to the magnets, but it's nothing more than a minor annoyance, and the magnets are strong enough to hold things in place, but weak enough to break the bond if I go too far and attempt to break one of the dials.

For what it's worth;

Another JohnS.

[David LittlewoodParticipant @davidlittlewood51847]

Terry,

My experience exactly matches Jason's. I fitted a DRO system (from Allendale, who I found extremely helpful) to my milling machine about 4 years ago, and now could not imagine being prepared to put up with a mill without it. It's extremely useful for milling, but it's absolutely indispensible for co-ordinate drilling.

I contemplated putting a similar system on one or both of my lathes, but somehow it has never seemed quite so important – I'd still want to test diameters in the traditional way, and the leadscrew handwheel on my S7 has always been perfectly good enough for turning up to a shoulder.

In theory you could share a console between the two, but it really isn't worth it as Jason said. The fitting of the scales themselves is quite critical, and they realy have to be dedicated to the machine they are on, so the saving would be minimal anyway.

I have looked with some bewilderment at those DRO systems which work by measuring the rotation of the leadscrew (the ones that look like overgrown handles), and I really can't imagine why anyone would bother. Unless you have a zero-backlash system fitted (which probably cost more than the DRO) then they simply cannot handle backlash, and therefore would seem to me to be worse than useless.

David

[JasonBModerator @jasonb]

John on a less than rigid machine would you need to allow for the tool being pushed off the work by different amounts if you were say taking a 0.050" cut to a 0.005" cut?

Also is it not more involved than just pressing the mill/lathe/grinder button if due to the way the scales were installed you have to alter their direction?

Plus you obviously need to have the console where it can be seen easily when working on either machine.

J

[SkarvenParticipant @skarven]

I started with a 2-axis Sino SDS6-2V for my mill and a 3 axes SDS6-3V one for my lathe. I missed the Z of the mill, and bought another SDS6-3V Universal Display Console – 3 Axis Display from Allendale. Later I have come to the conclusion that I could just have used the 3-axis on the mill and sacrifised the 3rd axes on the lathe compound. I now have a spare 2-axis Sino SDS6-V2. If you are interested I could bring it to Sandown on Friday

You could use only one console for both, it only take a few minutes to set the scale directions and resolution and a few other things. You will loose any scale zero-settings though, and I often find myself using the mill while something is set up in the lathe or the other way around. I would also use a switch to change over the two or three scales, and make a very good ground connection between the two machines to make shure nothing will go wrong.

The cost of the extra Sino display (Allendale) is £208 for the 3-axis and £167 for the 2-axis. The scales are from about £80 to £120, so the the total for 2 complete 3-axes systems will be aproximately £1000. You would save some money going for one display, and you can allways buy another one later if you find the changeover is to much. You will have to have dedicated scales for the two machines.

Kai

[Clive HartlandParticipant @clivehartland94829]

Just in the proces of fitting a 3 axis set to my new mill, total cost was approx £400 but I may have to go back with one of the scales. This an optical system as compared to a mag. tape system at over £590.

I have had to spend time machining the alu. brackets and plates true and square as they look like castings and are not square at all. Also had to machine a couple of extra slots to accomodate positions of existing screws on the mill being used.

Will also have to dismount the slides so that I can drill mounting holes on the rear of the 'Y' axis table base.

This is not a quick job and make sure you have enough M5 screws of the right length for the job. They dont supply those.

Clive

[blowlampParticipant @blowlamp]

The minus sign becomes important when you start to use some of the more advanced functions of the DRO, such as the PCD and radius facilities.

The positive or plus direction of travel is regarded as up for the Z axis, right for the X axis, and forward for the Y axis. These movements are seen from the operator's view at the front of the milling machine and apply to the tool movement in relation to the workpiece and not table travel direction.

As an example, and assuming that the cutter is zeroed on the upper surface of the part, this means that plunging the tool into the job in the Z direction will give an increasingly large minus number on the DRO display and can be confusing at first

Martin.

[Robin teslarParticipant @robinteslar]

The more I read the golden nuggets on DRO on this board, the more convinced I become that I am going digital eventually with a proper 3 axis system for my mill. I am going to play with a digi caliper on my lathe first to get the feel of the technology. For £10 its a good way to dip your toe in the suds

Robin

[Robin teslarParticipant @robinteslar]

Sorry pardon, I forgot to add (cant edit post here?). As one member pointed out , the old clock dial DTI is far from dead for cross slide work. Im sure I dont need to labour the point but there are now digital versions of the clock dial with exactly the same finger mechanism and fitting onto the usual magnetic base. Does anyone have any experience of using one of these.

To cite an analog, I once bought a digital multimeter thinking it might be quicker to read than my trusty AVO. Wrong

a) you can tell a lot about a test by the way the needle moves and it will average a noisy signal

b) a digital display tends to flicker about till you press sample hold. It was rarely the same as my AVO, and I know which I prefered to trust.

So I wonder if a digital DTI will have the same raft of draw backs?

Robin

[Captain BigglesParticipant @captainbiggles]

I've just added a 3-axis Universal DRO (from Allendale) to my Chester Centurion 3-in-1, and am using Renishaw / RLS 1um magnetic encoders.

I've used the Allendale 2-part tape support as well, a fantastic modification and one that means both the readhead and tape are totally sealed and can be doused in grease and swarf and coolant. I don't have to worry about bashing anything either.

The readout has transformed my performance. I'd hesitate to say it's changed the machine's performance as the back-lash and sloppy handwheels are all still there, but my ability to overcome these and produce accurate parts has been transformed!

As was mentioned above, even though the backlash is there, provided you've attached the scale and readhead to the correct parts of the machine, the DRO will always be reporting actual position. Things it can't compensate for are when the tool slips in the toolpost / collet or the workpiece slips in the vice etc. But if everything is held tightly, then if the table / toolpost move then the DRO will show this – then just wind the handle to compensate. Key to this is just to think about what's moving, and what the encoder is measuring. Get your head around this and you'll be fine.

DROs can't compensate for anything, so you still have to approach the same problems in the same old way, there's no substitute to age-old techniques etc. But the DRO will give you a much better idea as to what is actually happening, without having to back off & measure etc.

Finally, I'll add that of course a 1um encoder will not enable me to produce parts to 1um tolerances. I should imagine my machine has all sorts of slop and lack of stiffness that means I'd be lucky to get to 10um tolerances. But that's got to be an improvement on using Chinese handwheel scales!

I used to work for an encoder manufacturer, so I know a little about the subject and it meant I was able to get the encoders for free – the whole exercise has cost c. £250. But I'd recommend it to anyone.

[jason udallParticipant @jasonudall57142]

use 0.1 um CNC machines at work…still need to measure part to see what you have made …tooling/ temp./ materal ../ coolant all variables and to some extent part to part varible…..

Just saying..

.gets a bit mad when you have to put mic and part in "oven" prior to measuring…

[Robin teslarParticipant @robinteslar]

0.1um this is another planet and into the realm where a piece of rod changes its length depending on whether its horizontal or vertical. My brain just fried

Robin

[jason udallParticipant @jasonudall57142]

Posted by Robin teslar on 31/10/2012 16:02:59:

0.1um this is another planet and into the realm where a piece of rod changes its length depending on whether its horizontal or vertical. My brain just fried

Robin

Without being rude …of course a beam or rod changes length .etc. horisontaland Younges Modulus wins..Vertical its Hookes law…...

..But yes these resolutions on MC do seem infeasable…since they are often derived from encoders attached to lead screws and the unscrewing of the lead screw etc. is measurable.. esp when accelerating 2 tonnes of turret/ tooling around… but the MC I am talking about is '94 vintage ( 19 94 !) and has straingauges and reference bars etc. built in to null out thermal growth of the machine. but even carbide wears and parts get cut at differing sizes dependent on push off of the stock …

but yes 0.1 micro metre is done and measured.. ( mutters about finish and what exatly are we measuring anyway.. )..

btw 1 u m is 1000 nm or about two wavelengths of light.. limit of visability anyone?

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