Tuning The Mini-lathe DRO Handles
I added the Sieg DRO handles to my mini-lathe. They are a nice addition, but bring the usual problems - backlash or stiffness. I am trying to figure out how to fix this.
First step is to loosen up the DROs. They are sealed inside with silicone, very nice but it seems to make the devices stiff to turn. Don't need that, so I cleaned them out. Quite a big help.
The second step is the bearings. The DRO handle is also responsible for removing axial play in the screw. The cross slide has a secondary mechanism, but the handle is the big idea.
The problem is that tightening down the handle screw is also supposed to remove the axial play. The handle washer tightens against the end face of the shaft to keep the handle tight, and that aluminum bushing that protrudes from the DRO to eliminate the play. Too tight, and the DRO clamps down too tight to turn. Too loose, and the handle just spins on the shaft. There's really no happy medium.
I did sand down the bushing a little while I was learning. Everything runs freely, but my backlash is set at the amount I sanded off. I messed about with some thrust bearings, but don't have the correct size. they show the idea, but don't work - yet.
I am going to order some 12mm needle bearings. These should fit over the shaft segment that passes through the aluminum bushing and provide a bearing surface between the handle washer and the bushing. Dimensions are still critical, but not quite as bad as the original design. I'd like to get a thrust bearing on the back side as well, but there's no room on the cross slide and the compound might be tight.
|Here's the DRO on the bench. I have replaced the set screw with a 1/72 hex head. The originals are easily destroyed or lost. One mistake is to try to use the set screw to reduce axial play. It can do that, but is really bad at it. Its sole purpose is to prevent axial rotation. Steve says, put the set screw in the middle of the travel, so that the collar spring takes up any backlash.||And the bottom view.|
|Best way to remove the labels is to lift them with a sharp blade and then put a few drops of Un-du in there. The glue gives up instantly, but remains stick when it dries so you can easily re-apply the sticker. There are 4 screws under the bezel to remove, #1 Philips works great.||Once the display is loose, release the contact wedge with a small screwdriver. It just has to lift a little, too much and it will break. It works by being two-in-a-bed with the ribbon. There's a black rubber seal and a piece of fish paper to lose.|
|Cut around the silicone with a really sharp knife. It goes all the way round and across the top. You don't have to cut very deep.||Remove the four screws holding the digitizer together.|
|Push on the front axis, the digitizer will start to swing out. Go after any reluctant silicon with the knife. Clean it up and re-assemble. That disk is sprung. Reassemble. It should turn freely.||Here's the compound slide. There's about 22mm available for a thrust bearing, more if I grind off the end of the gib. Looks like I forgot to measure that hole, but it has to be about 15mm. McMaster 5909K13 maybe? 28mm od may be pushing it.|
what I am thinking for the cross slide. Doesn't work, the bearing is too
small. I am going to try 5909K11, a 10mm needle bearing. that's an M6
screw in the end.
To make this work, I need a spring washer for the bushing or the handle. maybe 94065K41.
|Same deal on the compound. Longer M6 screws accommodate more stacking. If this works, I'll have to sand the bushing down a bit more to expose more for the shaft.|