Monday, March 9, 2015

Lathe: QCTP Tool Holders

The inside bottom corner of the 0XA tool holder (and I suspect pretty much any other QCTP tool holder) has a slight radius. This helps prevent a stress riser from forming in the corner and a crack forming. However, this doesn't allow tool bits to rest against both the bottom and side of the tool holder.

Since I'm not going to mill a sharp corner in the tool holder for the reason above, this left remove the corner from the tool bit instead. Since I mostly use indexed tools I just clamped the tool in my angle vise at 45* and milled just a little amount off the edge. This gives enough clearance for the radius in the tool holder and allows the tool to sit flush against the bottom and side.

For my non indexed tool bits I just run the edge along the grinding wheel just enough to knock the corner off.

Edge milled off tool bit holder and sanded smooth.

Lathe: Setting Tool Bit Height

I had a hard time quickly and accurately setting my tool bit height, and finally found a solution using an old inch -only dial caliper I didn't use anymore. After chucking a piece of aluminum in the lathe I took a couple cuts. I then measured from both the top and bottom of the turned portion to the top of the cross slide. Averaging those measurements gave me the distance from the top of the cross slide to the center of the work. I then set my old dial calipers on end on top of the top slide and adjusted the outside movable jaw until it was exactly that distance from the cross slide.

Now to adjust tool height I set the caliper on end on the cross slide and adjust the tool bit until it just clears the outside movable jaw on the caliper.

Setting tool bit height. I want the bit to just graze the caliper as it slides under the jaw.

Lathe: Compound Slide Delete

There's more potential play in the compound slide than I originally expected. It because very apparent when my parting blade jammed in the work and I saw the entire compound rotate on the gib. Since I only use the compound for threading and cutting tapers, it made sense to replace it with a solid chunk of metal.

The clearance between the top slide and chuck center is 55mm, so I carried that clearance over to the steel block. I realized setting it up for the largest diameter work it could handle would compromise doing small diameter work (which is the majority of what I do), so I made the block reversible, hence the two set of screw holes. The back of the block is relieved at 22* for work clearance when in the large diameter position.

In large diameter position.
In small diameter position.

To better support the QCTP I took a 3/16" hot rolled steel plate, milled top and bottom flat, and cut a shallow channel in the bottom the same width as the top of the steel block, keeping it positioned side to side.

It uses the existing compound mount, which also makes re-installing the stock compound slide very easy. The new setup works very well and has noticeably increased the rigidity of the lathe.

With 0XA QCTP mounted.

Friday, March 6, 2015

Cold Rolled Steel

I learned a lesson the hard way on using cold rolled steel. There are tensile stresses in the skin of the steel extending 0.5mm to 1.5mm deep. So if you do anything other than just drill holes, the steel will warp in some interesting ways. If you are going to use cold rolled, then you either need to stress relieve it (which is hard if you don't have a forge or furnace) or you need to mill at least 1.5mm off every face.

Instead of using cold rolled, from now on I'm going to use hot rolled steel which simply doesn't suffer from this.

Tuesday, March 3, 2015

Mill: Y-Axis Gib

Please read the complete article:

Substitute the mini mill Z-axis gib for the Y-axis gib. You'll need to cut it to length, but the Z-axis gib sits much better and takes up nearly all the space available.