DRO Kit for the Myford ML7
I was talking to a friend at the club a few weeks back and we got to talking about DROs for the lathe. The next morning I thought 'you know what, I'm going to get one for the ML7'. The one on the mill has been a godsend and I'm sure that one for the lathe will also be well worth while. So, I ordered a kit from MachineDRO which is specifically designed to fit straight onto the ML7. They were out of stock at the time but I preordered one at a slight saving in cost. I could have got a cheaper kit from China as I did for the mill but I thought that it would save time and effort to get a purpose designed kit that should just bolt on.
The older style kit, which they still do, has the cross slide scale bolted onto the tailstock end of the saddle and it interferes with the available travel of the tailstock which can be a nuisance. However, you can now get a kit which uses a magnetic strip fitted under the cross slide so the tailstock travel is unaffected so I went for that kit. This does involve machining a slot in the underside of the cross slide to take the magnetic strip for the scale so may not suit the 'purists' who faint at the very mention of drilling holes etc. in their precious machines!
The well packaged kit arrived today and I was surprised at the number of bits. I was expecting less considering that it is only for two axis.
Parts as packaged:
The brown envelope contains the magnetic scale for the cross slide and the mounting brackets for the reader.
There are numerous brackets supplied which I presume are for mounting the Z axis scale and reader to the lathe bed and saddle and a comprehensive set of fitting instructions.
I'm not sure when I will get around to fitting the kit but it could be fun as it would be much easier to have access behind the lathe which I don't really have at the moment. I think that everything fits to existing holes in the back of the bed so I can probably do it all from the front by just leaning over. If that doeasn't work then I may be able to drag the lathe stand out at the tailstock end to give me better access.
One thing I will probably have to do is reorganise the wall behind the lathe to make room for the display console. At the moment my most used tools are on racks screwed to this wall so they are within easy reach. I've also got to find room to fit the box containing the electronics for the electronic leadscrew project although that can go anywhere within reason.
Today I completed the installation of the DRO kit following a couple of afternoons work and it's all working nicely apart from the X axis is reading backwards so I need to read the instructions to find out how to reverse it!
The installation was pretty straightforward thanks to the clear instructions and it should be possible for anyone to complete it in a day.
The Z axis scale fits to the back of the lathe using three brackets which bolt on using three of the existing threaded holes in the bed. I think these were originally intended for mounting a taper turning attachment so I presume that you can't fit this kit of you have one of those and intend to keep it.
The actual scales are a length of magnetic rubber strip held in place with 3M double sided tape and then covered over with a thin stainless steel strip to protect them. The Z axis scale also has an aluminium cover to keep swarf etc. away from it.
The Z axis reader head is mounted to an aluminium extrusion by two brackets. The extrusion is bolted to the back of the saddle using two brackets bolted into the existing threaded holes for fixing the rear saddle clamp.
Mounting the X axis scale involves drilling and tapping two holes in the rear of the cross slide casting. These are used to mount an aluminium extension block to extend the magnetic scale further back.
For drilling and tapping the holes I mounted the cross slide casting to an angle plate on the bed of the milling machine and then dialing it in to make sure it was square to the ways.
I had to raise the head of the mill as high as it would go to get enough clearance for the drill and then it only just made it.
The extension block was then bolted on.
You then need to mill a 10mm wide by 1.8mm deep slot into the underside of the cross slide casting and the extension block to take the magnetic strip. This was easily done by clamping the casting directly to the mill table and dialling it in to align it with the X axis of the table.
I found that the magnetic strip was actually 10.2mm wide so I had to make my slot cut with a 10mm carbide endmill slightly wider before it would fit. The strip is simply stuck down in the slot with double sided tape and a thin stainless steel strip stuck over it for protection.
With hindsight the slot doesn't need to extend as far across the casting but I just made it the same length as the supplied strip.
After refitting the cross slide to the lathe the X axis reader can be fitted. This just bolts to another bracket which is in turn bolted to the aluminium extrusion on the rear of the saddle.
The display was mounted behind the lathe using the supplied arm which was screwed to one of the window frames to get it high enough.
Fortunately I didn't need to move any of the tool racks behind the lathe as first thought. I may shorten the arm as it is longer than needed for my installation.
The cables were then tidied up as best I could but they are far too long really and I've got a big loop hanging down behind the lathe stand. I would shorten them but that would no doubt invalidate the warranty. You do need to make sure that there is plenty of slack in the cables as they need to move as the saddle moves up and down the bed.
Overall I'm very pleased with it and it certainly didn't take long to fit compared to the DRO for the mill where I had to machine brackets etc. The only thing I don't like, and I don't know if this is intentional or not, is that the X axis won't read the total travel of the cross slide. When you wind the cross slide out, after about 3 inches of travel the end of the magnetic strip goes past the read head and consequentley stops reading. My cross slide has another 1.75" of travel after that before the feed screw disengages from the nut. If I'm turning a large diameter then I don't think I will be able to use the DRO to read the X axis position. To do this, the extension block on the rear of the cross slide needs to be about 2 inches longer so that the scale can be moved further back. It would then align with the read head all the time throughout the whole cross slide travel. If this does prove to be a problem then I will fit a longer extension piece and move the magnetic strip further back, assuming that I can get it unstuck from the slot in the cross slide again. I can always get another magnetic strip if I couldn't get it unstuck without damaging it.
Now I've just got to read the instruction manual and learn how to use all the functions!