Author Topic: DRO Fitting To A Lathe Tailstock  (Read 5921 times)


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DRO Fitting To A Lathe Tailstock
« on: October 25, 2012, 08:32:38 AM »
Another of my transfer posts, but this time, there are a fair amount of hints and tips in the post that could be used elsewhere, so you will have to get bored and read the lot.


This all started a few years ago, when I installed my then new lathe, and decided to fit a couple of extra DRO's, one on the compound and another on the tailstock, to compliment the two it came with. Once you get used to the accuracy of using something like this, you soon realise that drilling to 'accurate depth' under normal situations is not very accurate at all. More like a disaster waiting to happen.

On the tailstock, I had machined a rail carrier for the glass slide out of ali, and had it running on four ball races. Unfortunately over the last year, swarf had found it's way into the top channel, and the rollers had then forced and embedded it into the aluminium. When you operated the tailstock by the handle, you didn't feel anything, but once the rail was disconnected from the tailstock ram and slid along by hand, it felt rough as old boots. This will only get worse, so I have decided to relocate the assembly to on top of the tailstock and make the rail out of a more durable material. Then I should be able to protect it a little better than I had done before.

This is a picture taken before I set to work.

Ten minutes had the tailstock almost back to original.

This is the old ali rail, and a lump of Ralph's 'garage special' to make the new one out of.

As usual with this sort of un-named material, it isn't very happy at being reshaped. So I had to persuade it a bit with a tungsten tipped shifter. Nothing too critical at this time, just cut down to split the line.

After hacking all the rough outer off in the last episode, the first thing I did was mount it up onto the surface grinder and gave it a lick all over.

Isn't it marvelous what is inside such a crappy looking lump of iron.
It gives you a feeling that you want to do more to it now, rather than struggling with the old outer casing.

Even though it looks like a nice piece of material, it is still the same old lump of tough stuff, and I have got to cut some very accurate 4mm slots in it.
It all starts by getting the cutter into the right position and taking a shallow cut (0.75mm) down the rail. This is a 3.5mm cutter, and the stripe down the rail is high pressure cutting oil (tapping fluid) to help with the cutting.

This is getting ready for the return run. The depth has been set to 1.4mm, oil down the groove and the return run was carried out. Once that was done, the operation was repeated on the other side.

So now that I had my two channels, a 4mm cutter was fitted and set to a total depth of 1.5mm. This will skim the two side faces and the bottom of the groove. Same again, oil was used and a fast cutter speed with very slow feed.
In fact each of the slotting cuts took 15 minutes each. Thank goodness I have power feed, an hour and a half of slow cutting would have almost killed me if I had to do it manually.
Also, by taking it easy, both cutters lived to cut another day.

The four end corners were nibbled off with one of my little hogger cutters.

All that long steady machining had really paid off. The bearings were a perfect fit in the slots, with only the merest hint of side play.

A little relief was made in the side to allow for a modified fitting regime. By doing this, I can squeeze the complete read head width up by as much as 15mm compared to the previous fitting. Also a couple of mounting holes were drilled and tapped to 4mm.

This picture actually proves that you can make a silk purse out of a pigs ear.

The original rail is in the middle, the new silk purse at the bottom and what bolts onto it at the top.

That is the boring stuff finished.

Here is a mock up of how easy it is to put a DRO on your tailstock.

It is in fact a tiny bit more involved than this, but basically it consists of a chopped down digivern (you can grind off all the sticky out bits), something to lock around the nose of the ram and you would need to make up either a sliding joint as I have or something like a small conrod to join the nose clamp and the digivern together. You need that joint between the two, because the digivern will be fixed rigid and the ram is guaranteed to have a slight rotation in the tailstock. If the joint isn't there, your read head would soon end up bent and buggered.

Anyway, back to fixing my bit.
By trying the slide I had made and the read head onto the top of the tailstock, plus some very accurate measuring of bearings in slots, I got the layout of where the bearings should be located.

The first thing to be done was securely clamp the tailstock onto the mill table, and by running a DTI along the ram, I got the ram perfectly parallel with the table.

Using the edge finder, I soon had the position of the first datum point. I wasn't worried that I was taking a reading off a painted edge, as it wasn't too critical where the first datum ended up, a few thou either way isn't going to cause any problems at all. The critical measurements are all taken from that first datum point.

At that datum setting, everything was zeroed up.

Before you all start screaming about using a milling cutter in a drill chuck, which is a very bad practice. This time only, all I am doing is skimming thru the paint layers and a superfine skim on the casting. These are going to be where the bearing spacers sit down onto.
If you notice my previous effort on the side of the tailstock, you can see where the spacers had cut thru the paint by themselves. This time, with a little more foresight, I am doing the job correctly.

The holes were soon centred and drilled for tapping to 3mm.

Then quickly followed down with the tap. Even though it isn't really necessary in cast iron, I did give each threading cut a touch of cutting oil.

With bearings tightened into the newly cut holes, the slide was tried for fit.

Even though I am running mainly on the bearing edges and faces, the slide is incredibly smooth in operation with no detectable side or up and down end float.

That will do me for now.

It took a fairly long time to get these four holes drilled and tapped, but this is a critical part of the setup, getting this slide running perfectly in line with the ram.
Besides, if a job is worth doing, you should do it to the best of your abilities and facilities.

All further fitting and drilling of this part of the mod will be done on the lathe, freehand.

This might be interesting for those of you who are contemplating fitting DRO's at some time in the future. Not onto the tailstock, but general information about fitting them.

As you can see, I have screwed the glass scale (GS) and the read head (RH) back onto the new slide, but this is a long way off being useable. These DRO systems do need to be set up very accurately to get long life and accuracy out of them. I have physical edges that were realigned between the GS and slide so that I know it is running perfectly parallel to the ram. Normally you have to use a DTI to get either the GS or RH running exactly in line with whatever axis you are fitting it to.

You have a choice when they are fitted, you can have the RH moving with the axis, as I did on the Z axis of my mill and the GS is fixed to the machine. The other way is to have the RH fixed and the GS moving, as in this setup.

So now back onto this setup.
When they are bought, the two parts usually come joined together with transit clips. So always save them, just in case you have to do something like I am doing, or they have to be returned to the supplier for checking or repair. Without them, there can be very serious damage caused internally to both parts, so they should always be in there and are the last things to be removed before turning on. They also act as setting guides, I have found that in this fixed position, if everything is fitted around them first, the gaps are perfect for normal operations.
The RH has to be set so that it never reaches the ends of the GS, so if you look very carefully, there is an arrow on the centre of the RH, and two dots machined into the GS. The arrow should NEVER go past either of the dots. Again, ignoring that can cause internal damage to the unit.
When you buy these scales, it is the distance between the two dots that is the read length, so as you can see, the GS are a lot longer than the actual reading length, and that must be taken into consideration when fitting them. The GS can be shortened, but that is maybe a discussion for another day
So I have set up my combo with the transit clips and the RH well within the 'dots', even when the GS is in the fully forwards position. Only now can I think about getting the RH clamped down.
I will be able to utilise the top piece of ali, but the other part of the holder will have to be remade.

So a quickie machine up of the one under the RH, and I also made a new one to clamp down to the tailstock. These two need to be joined together.

More boring machining piccies.
This one shows the use of the edge finder and vice stop to get the holes where I wanted them. The holes are unique to every individual fitment, and can only be determined by fitting it to your machine and measuring up.

The holes being drilled. Do the first, then flip it over to do the second keeps everything nice and symmetrical.
The same method was used for the bottom block.

These are the two finished blocks. All that needs to be done is the larger one has to have the four corner holes tapping out to accept long flat faced grub screws. They are needed to align the block onto the uneven surface of the painted tailstock before it is tightened down.

Now that I had the holes in the top mounting plate, it could be bolted onto the RH and then the bottom plate positioned where I wanted it.
It was then a matter of hammer tapping the hole positions thru with a transfer punch. The bottom plate was then drilled and tapped to take the joining screws.

So now having the final position of the bottom plate, I marked up where the jacking screws were situated.
Now comes the time to upset people you don't really like.

Go around to your neighbour and ask to borrow his sharpest brown stuff chisel.
Then take it and duly hammer away thru the paint layers until you hit base metal. Then scrape the surface well to get rid of all the paint.
He will really thank you for what you did to his chisel, and if you are lucky, he won't talk to you for months, or until he wants another job doing.
You need this area for the jacking screws to sit on. If you dropped them onto the paint alone, it won't have enough strength to keep all the work you have done stable. It would be rocking about in no time.

So now was the time to use the jacking screws to get everything perfectly set. It has a lot to do with feel.
As you screw them in, you will feel them touch the bare metal underneath, then it is a matter of individual tweaking to get the RH supported, but not moved out of the position that the transit clamps have put it into.
Once that stable position has been reached, it is then a matter of transfer punching thru the hole locations.

The marked holes were drilled and tapped.
If you do have the facilities to use a straight drill, then I find them much easier to keep the hole square when drilling vertical.

Maybe it comes from all the rivet holes I drilled on aircraft, I always found that the straight drills were the first ones to go out out of the tool cabinets. It also seems aircraft fitters prefer them as well.

Once it was all tweaked up and cleaned down, that is this part finished.

The next bit is to get this lot being moved by the tailstock ram.

Now comes the real wing it bit, I have to make a fitting to go around the ram and then connect to the end of the slide I have made.
Up until now I have used metric measurements for what I have done, but because my boring head is imperial, the easiest way for me is to work in imperial for this one part.

So after a quick measure up, I did a sketch that would get me in the ball park. Then after that is done, I will trim it down to final shape. The piece next to the pad is the original, so as you can see, it is nothing much like the one I am going to make, except for the slot and big hole.

It didn't take long to get it scratched out on a piece of ali 1/2" plate.

It didn't take much longer to hack it out on the bandsaw.
Unfortunately, I have four sawn edges, so it cannot be held safely in a horizontal position in the mill vice.

That was easily remedied by flycutting two opposing edges parallel to each other.

Now it could be clamped safely in the vice, the backstop and parallels came into action again. The backstop was a safety precaution, to be able to take the part out of the vice and be able to reposition it again if it wouldn't fit the ram.
The centre of the circle was zeroed up and X & Y axis were locked up solid.
By going up in a couple of stages, I managed to get a 1" drill thru it.

The boring head was now swung into action and the hole was gently opened up to size. It really is a treat to have power feed on the Z axis, it was just a matter of putting on a cut, a quickie spray of WD40, then flick the handle and park my bum while it did the work for me, both up and down.

I was soon out to the required measurement of 1.258" plus 0.002" for clearance.

It fitted perfectly, so the backstop wasn't required, and it looks like I did something right for a change.

Lots of piccies this time for you to root thru and see if you can pick any tips out of this lot.

I ended last time where I had just got the hole bored thru the nose clamp.
I have removed all the gubbins off the rail, blued up the back of the plate then got it vertical to the lathe bed, then it was marked up where the rail was in position against it.
These lines were transfered to the front of the plate.

I quickly got rid of all excess material, and ended up with still one machined face, the one under my thumb.
This face will be very helpful when I get it onto the RT.

Just checking to make sure I haven't taken too much material off.

First the RT was zeroed to the quill and the table was set to zero degrees.
A washer on each jaw face is to give me clearance for the cutter tip, otherwise I might be milling the chuck jaws.

The part was set down onto the washers and the jaws lightly nipped up.
Then by turning the part, I tracked and adjusted the machined face until it ran parallel to the table.
The chuck was then tightened up and the washers removed.

Because I had set the RT to zero degs meant that by turning the table I could get right angles and parallel cuts to the original straight face. It really made shaping this part up a piece of cake.

Done in no time.

A little bit of vice work soon had everything in the right position and almost ready to fit.

On the previous plate, I just had a straight hole. This time I will be attempting to reduce any wear. I made up a brass bush with a smooth faced flange on it and a smooth faced brass washer to go under the spring.

I fly cut the face which was to have the flange sitting against it.

The brass bush was locked in the hole with fast setting hi strength Loctite.
Ten minutes later, I flycut the second side and the bush down to the same level.

The clamp plate was fitted and locked up, then using a transfer punch, the hole centre was popped onto the end of the steel slide.

I hate four jaw work with a passion, but it had to be done. So using the old method of two centres and a DTI, the pop mark was centred up.

I soon had the hole drilled and threaded.

Very quickly, it was all bolted up and ready for trials. The hole thru the plate is 6mm and the screw going thru it is 4mm. So there is plenty of free space to allow the ram to rotate. The slip joint worked just as well as the first time I did it.

After giving it a good try out, the DRO works faultlessly.
By having the head in this position does make it more vulnerable to damage, so I have devised a way to protect it and also make the cover into something useful.

I am using some of my black 10mm thick perspex.
I love working with this stuff, if care is taken, it is very easy to machine and the results can be great.
This is having some 10mm flutes machined into the face.

The table is getting a bit crowded, with an RT and two vices. This is just a temporary one that I am using to put a 5 degree angle down one long edge.

Two parts done, two to go.

A very black time in the shop today, finishing off the cover for the read head.
The reason being I was using this dense black perspex I was given, it seems to absorb all the light and you just can't get good detail in the pics.

The fist job was to get everything glued together.
This was a major H&S issue, the chemical liquid I was using required the whole lot, mask, rubber gloves and glasses and applied by the drop thru a syringe.
But it does have the advantage that it is a fully bonded joint within 10 minutes and so it could be stuck back onto the mill for a bit more work. I have tried all sorts to get a good bond on perspex, and this one does it.

Up onto the mill to have the top faces evened up and a radius put onto the top corners.

A bit of polishing and a few holes drilled, and it was ready.

No clearance issues anywhere, and it seems it could stand a tank running over it.
It will even hold a few small drills or whatnots on the top.

Job done and dusted.

Maybe people are wondering why I have gone to all this trouble just to drill a hole.
When you have a drawing in front of you that states the hole has to be say 1.478" deep, this allows me to do just that, nothing more, nothing less. It gives you greater control of your machine.