I got a Shars OXA tool post for my Atlas 618

[mvagusta]

A while back when I was looking for something to do, I decided to purchase a Shars OXA-000 Quick Change Tool Post (QCTP). My Atlas 618 didn't come with a tool post. This one is made in China and is an interesting blend of nicely and poorly machined component features, resulting in a tool post that is no more than workable but perhaps not the worst choice I could have made. On the other hand, being built where it was, my expectations were not high. It looked like this:



I ordered 3 things that came nicely packed in one box:

Shars OXA Wedge Type Quick Change Tool Post Set 250-000 S
Shars OXA #2 Quick Change Boring Turning Facing Tool Post Holder CNC 250-002
Shars OXA #1 Quick Change Turning Facing Tool Post Holder CNC 250-001

The set comes with 5 tool holders and I ordered a few extra tool holders. I got them off of eBay from Discount Machine Shop, which is Shars' store on eBay. The parts can be ordered online directly from Shars, but their eBay prices are lower. They also combine the shipping if you request it.

Each component arrived in a sealed plastic bag inside its own box and when removed from the bag all the parts were dripping with oil and had to be wiped down. I bet there was a problem with rust some time in the past. No chance of that these days.



Each item also came with a certificate of compliance. However, it does not state exactly to what it complies. But whatever it is, I am assured in knowing that it did not fail to comply. Perhaps it is a Borg thing.

The as-delivered tool post did not operate smoothly at all and it was clear that some hand work would be necessary, so I would have to take it apart and get out my hand files.

 

[mvagusta]

Once the tool post was disassembled there was something that came as a surprise. The threads on the wedges were cast, not machined, and had a textured surface. That probably doesn't help the smoothness or lack thereof. The photo below shows one of the wedges and what I call the screw actuator. The deburring had already begun at this point but wasn't close to being finished. If you look closely you can see the casting texture in the thread surfaces.



This photo is a view of the body block from the bottom with the dovetail wedges inserted in their T-slots:



The T-slots are machined at something like a 4-degree angle relative to the bottom. Note that the left edge of each wedge is sticking up higher in the T-slot than the right edge. The right edge of each is actually below the surface while the left edge is slightly above.

Here is a closeup of the screw actuator:



The screw is a triple-lead, non-standard trapezoidal metric thread. It looks like ACME but it's not. It was difficult to determine exactly what it is, but my best guess is M28 x 5.5 triple-lead.

The wedges are fairly complicated parts with multiple compound angles and trapezoidal threads that are at markedly different lead angles. Here is a photo of one of them:



The plane surfaces are ground. All the tooth profile edges had to be deburred with a jeweler's file and a Dremel with a wire wheel. Several other places on the wedges needed attention as well.

 

[mvagusta]

Here are all the parts after deburring was complete:



The parts that needed the most attention were the body block, the screw actuator, and the wedges.

Below are some photos of the individual parts.

Here is the retaining sleeve that holds the screw actuator in place:



Note that the thread is left-handed, so it must be removed by rotating clockwise. Righty-loose-y instead of righty-tighty. A 7/8" wood-drilling spade bit makes a convenient removal tool.



Here is a closeup of the machining on the OD of the sleeve:



Pretty cobby. I could use it for a fingernail file. A general rule of thumb for this tool post appears to be the machining and finishing quality is only decent if it is visible from the outside.

Here are the wedges:



Because the photo is taken from slightly above, it is hard to tell that the one on the left has threads that are around 8 degrees steeper in lead angle than the one on the right. These were labeled "1" and "2" so that they would be put back in the correct slot on reassembly, but it wasn't really necessary. If they are put in backwards the actuator locks up in a small fraction of a turn. It's also pretty obvious by how the wedges are not aligned in dovetail fashion.

Here is the actuator:



The threads required quite a bit of trial-and-error deburring work before smoothness in operation was achieved.

The T-slots required a good deal of deburring as well:



Every edge needed to be deburred. The interior edges were a bit difficult to get to and to do, even with a jeweler's file.

 

[bill stupak]

Nice work, should make a nice addition

 

[mvagusta]

Thanks. After I have stripped and repainted my lathe (that I also took apart), and put it back together I will actually get to use this tool post.

Also, while I had the tool post apart I measured everything and created a 3D model of it.



Here is how the parts go together:



For those who have CAD systems, I uploaded the CAD model in STEP file format to the new Cad Models area of Downloads.

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