DRO for a CVA lathe

[fizzy]

Why do I need one? Because the lathe has metric dials which I really don't like. My Colchester has imperial no problem
Just been reading @Pete. Brilliant thread on his 10EE.
I know they are very similar. Big question though. How do you fit the DRO to the cross slide AND still be able to use the weird travelling steady

 

[Martin-Sy]

Did it for mine like this after seeing a Myford ML7 done this way.

This is using the magnetic type with read head and tape supplied by M-DRO.
The tape is in a rebate in the alloy strip with s/s shim cover stuck over it.
Mine does not have the TTA and I don't think this would work if yours has.

The lathe came to me with a DRO but it had not been very sympathetically fitted.
The optical scale prevented the traveling steady from being fitted and the rear splash guard was bent back to clear it at a stupid angle.

How are you liking yours?

 

[fizzy]

Did it for mine like this after seeing a Myford ML7 done this way.

View attachment 340376

This is using the magnetic type with read head and tape supplied by M-DRO.
The tape is in a rebate in the alloy strip with s/s shim cover stuck over it.
Mine does not have the TTA and I don't think this would work if yours has.

The lathe came to me with a DRO but it had not been very sympathetically fitted.
The optical scale prevented the traveling steady from being fitted and the rear splash guard was bent back to clear it at a stupid angle.

How are you liking yours?

That would work. Sadly no taper Turner with mine.
I haven't had a chance to use it much yet as I have been ill.
Had a play around last week and again today.
Runs very smoothly. Loving the 5C collet chuck and drawbar.
Turned a test piece about 12" long. Used a live centre. Accurate to within about half a thou so far.
Still love my old Triumph roundhead though.

 

[fizzy]

Did it for mine like this after seeing a Myford ML7 done this way.

View attachment 340376

This is using the magnetic type with read head and tape supplied by M-DRO.
The tape is in a rebate in the alloy strip with s/s shim cover stuck over it.
Mine does not have the TTA and I don't think this would work if yours has.

The lathe came to me with a DRO but it had not been very sympathetically fitted.
The optical scale prevented the traveling steady from being fitted and the rear splash guard was bent back to clear it at a stupid angle.

How are you liking yours?

Some more piccies and info on your dro would be great.

 

[Martin-Sy]

Ok, will get some more pics & post here. ISTR i actually did some drawings for the tape and read head mountings. Both made out of what i had in the odds bucket.

Yes, I saw you'd been unwell. Hope you're fully recovered. That sounded very nasty.

Collets: I'm jealous!! Mine came with a full set of holes where the collets should be, but a mate put me on to a set of Burnerd multi-grips with the front lever closer. Just need make a new base for the closer anchor to suit the CVA bed. I think it came from a Colchester.

 

[fizzy]

Can you use a magnetic scale on 1 axis and an optical on the other?
5C collets are great but the gripping range is tiny - you need loads of them - which luckily I have from another lathe as well.

 

[Pete.]

You can use any type of scale that talks the right language to the head unit. Most of the Chinese type are 5v TTL quadrature scales .

 

[Agroshield]

Another small form factor scale is the Newall microsyn range. Very costly however, but useful to know about if other options do not work out.

Try to find the manufacturer's drawings for the magnetic scales and reader head (for conventional ones, Sino's native site has good literature - you need to find the OEM for the magnetic ones and find their site). Then you can make a mock up in wood and test for fit.

If you can post a picture of the machine dressed up with its steady, and maybe with the cross-slide removed so we can see saddle and underside of cross-slide), it might bring forth some ideas.

 

[Pete.]

If you have a quick change tool post you might want to see if the travelling steady actually works with it because a lot of them don't leave room for the tool holder they were designed around 4-ways or lanterns.

 

[Martin-Sy]

Can you use a magnetic scale on 1 axis and an optical on the other?

Yes, as @pete says provided the interface is the same the readout does not care.
The M-DRO ones are quadrature logic level outputs. The old Accurite optical scales that were on mine were also quadrature.
What you would need to check is that the readout can be set for the correct scale resolution, and maybe different resolutions for X and Y if the optical and magnetic scales are different.

If you have a quick change tool post you might want to see if the travelling steady actually works with it because a lot of them don't leave room for the tool holder they were designed around 4-ways or lanterns.

This seems to be OK. My CVA came with a Dickson toolpost which is alright with the steady in use.
Couple of pics below. Almost the last thing I did on it before starting the rebuild.

The magnetic scales that M-DRO supplied were made by Balluff.

Magnetic encoders | Balluff

www.balluff.com

They can be cut to length easily.
BTW, my CVA is metric too. (well the cross and top slides are, but the apron movement dial, is imperial and leadscrew/threading is also imperial).
Cross slide dial 'lies' and gives diameter change rather than tool movement. I much prefer tool movement.

I will sort out more details of my install for you later today when I have a bit more time.

 

[fizzy]

Yes, as @pete says provided the interface is the same the readout does not care.
The M-DRO ones are quadrature logic level outputs. The old Accurite optical scales that were on mine were also quadrature.
What you would need to check is that the readout can be set for the correct scale resolution, and maybe different resolutions for X and Y if the optical and magnetic scales are different.



This seems to be OK. My CVA came with a Dickson toolpost which is alright with the steady in use.
Couple of pics below. Almost the last thing I did on it before starting the rebuild.

View attachment 340419

View attachment 340420

The magnetic scales that M-DRO supplied were made by Balluff.

Magnetic encoders | Balluff

www.balluff.com

They can be cut to length easily.
BTW, my CVA is metric too. (well the cross and top slides are, but the apron movement dial, is imperial and leadscrew/threading is also imperial).
Cross slide dial 'lies' and gives diameter change rather than tool movement. I much prefer tool movement.

I will sort out more details of my install for you later today when I have a bit more time.

Fantastic info thanks.
I really did get lucky with this lathe.
Seems to be very little wear.
Quiet running.
I didn't realise it came with so many extras. Full set of collets - collet nose piece and drawbar. Fixed steady. Travelling steady. 3 and 4 jaw chucks. Faceplate. Dickson post with 5 holders. And what I think is a full set of metric change gears!
Only real fault was the leaking oil seal on the bottom pulley which I have now fixed.

Another question - where do you fill/clean/drain the coolant sump from?

 

[Martin-Sy]

Here are some pictures and a couple of drawings for the read head mount and for the mag tape mount.
The underside of the cross-slide has a rebate at the far end:

I have drilled and tapped four 2BA holes, but there are no other modifications to this.
The tape backing support strip was machined out of a bit of 1/2" alloy plate that was in my scrap box.

I wondered about using alloy here as it's thermal expansion co-efficient is high, but I did sum sums and I don't think there would be sufficient expansion to worry about.
And on the plus side....I also wondered about what happens when I put a DTI on a mag base directly above it.
With an alloy backing the magnetic flux will mostly stay in the cast iron which would be better than if the backing had been ferrous.
ISTR I asked M-DRO about this and they said it's OK even with a ferrous backing. Certainly ML7s have the tape milled into a slot in the cross slide.

This is the off-cut of the encoder tape. It's 10mm wide and a couple of mm thick.

Here's a view on the end. There are two slots.
The narrow one has the tape (self adhesive backed IIRC), and the wider one has a bit of 10 thou s/s shim glued in as protection.

Now the read head mount.
On the back of the cross slide there's a square plate which holds the two cross-slide lock binder bars.
It's the lower item in this picture.
I replaced it with one that also holds the read head. Upper item in the piccy.

There's a drawing for this attached but having made one I would not recommend it.
It's a lot of hacking on something that's not easy to hold.
I reckon just a piece of plate stuck on the original part, or a fabrication, would be much simpler and quicker.

Your question on draining the suds....That will depend on whether yours is a series II or a series III.
Series III have the suds pump mounted vertically on the rear of the bed casting.
Here's mine:

The cover plate in the picture can be removed to drain/clean out the 'tank'.

On series II machines the suds pump is in the rear cupboard but I don't know how the suds on these is drained.
Please let me know which series yours is. From the s/n I think it's close to the point where they moved to series III.

Did your accessories include the rear tool post base?
It's a dovetailed block that fits on the back of the cross slide with a T slot for a tool post.

 

[fizzy]

Thanks for all this brilliant info - much appreciated! What length ribbon do I need?
Mine is the same as yours - vertical pump.
Not sure if there is a rear toolpost base - don't think so.

Where are you with the rebuild now?

 

[Martin-Sy]

Just found the invoice. I had 250mm of tape with 5 micron resolution. Obviously I had a bit left over 'cause that's in the piccy above.

Mine: Apron is currently in-progress (which is pedestrian compared to some folks here )
There's more detail on Practical Machinist in the Monarch forum which I tend to regard as its 'ancestral home' but I now have two aprons completely dismantled and will be picking the best bits for mine.

One interesting thing coming to light is that the half nut mechanism is prone to damage from heavy handed operators that don't realize the feed reverse MUST be in the centre (neutral) position.
You might want to check that both upper and lower half nuts move on yours. I guess it would still work with only one of the half nuts engaged but the interlock works only on the bottom nut and this can happen:

This is the 'spare'. Today I looked more closely at mine. It's been repaired here too.

 

[RichardM]

@Martin-Sy thanks for posting that, good option for my Boxford 280 too.

 

[bletchmonster]

I bought an Easson dro display off M-dro for my mill and its way ahead of their m dro badged unit I have on the lathe for not much more money It has "homing" ability built in but the magnetic scales they supplied don't support it. I think the reference points for homing are available on the glass scales.

 

[Martin-Sy]

There's a good explanation of the principal and of the pros/cons for magnetic scales here:

Magnetic DRO Scales

The read heads are significantly more complex than those for optical scales.

 

[fizzy]

There's a good explanation of the principal and of the pros/cons for magnetic scales here:

Magnetic DRO Scales

The read heads are significantly more complex than those for optical scales.

I wondered why they were so expensive. The devil is in the detail.
In theory they are nothing more than an old fashioned audio tape and head
It seems to me that part from the compactness optical heads are a far better option.
Wouldn't it be possible to mount an optical track at the back of the cross slide in a similar fashion to your setup.
Just have the rigid part firmly attached and moving in and out. Think of a digital vernier attached to the cross slide at the very back and sticking out a fair way.

 

[Martin-Sy]

As I see it the pros for mag scales in this context are:
1) Compactness.
2) Simplicity of protection from swarf and cutting fluid.
3) Ease of trimming to just the right length.

Yes, I think you could do it optically as you suggest, but the scale will stick a long way out ( total cross slide travel plus a bit).
I think that's going to be about the same whether the scale or the read head moves.

Yes, I agree that optical seems inherently simpler and less susceptible to external influences.

 

[fizzy]

As I see it the pros for mag scales in this context are:
1) Compactness.
2) Simplicity of protection from swarf and cutting fluid.
3) Ease of trimming to just the right length.

Yes, I think you could do it optically as you suggest, but the scale will stick a long way out ( total cross slide travel plus a bit).
I think that's going to be about the same whether the scale or the read head moves.

Yes, I agree that optical seems inherently simpler and less susceptible to external influences.

I will check if there is clearance with the splash guard. Won't look very pretty though and needs to be very rigid with that much stick out.