G0709 for mcdanlj

[mcdanlj]

I hated the piston-style QCTP that came with the G0709, so I bought a wedge-style QCTP from Precision Matthews, along with a pile of tool holders.

The QCTP bolt that came with the original didn't fit the new one, so I had to come up with a new solution. I had a 1/2" x 2" piece of CRS stock, and milling slots along the top made it a perfect slide fit in the compound. Drilled it to 37/64" in the center, tapped it 5/8-18, and it was much better than the original.

But I hate wrenching the 1" nut on the top. Eventually I decided to make a wrench-optional nut. I had the drill and tap already, so why not?

I made a part 1.6" at the bottom, with a 20⁰ taper for the handle to keep it out of the way of the locking handle, and flats for a 7/8" wrench (same as I use to attach vise and dividing head to the mill next to it) at the top in case I get too enthusiastic tightening it down. Made six threaded sockets for the handle to make sure I can always find a convenient location; it wasn't much more work to do six than one anyway because I already had it in the dividing head for cutting the wrench flats. The dividing head was a convenient way to hold it at 20⁰ and turning the dividing head a few times is easy enough. The wrench flats on the nut are a bit imperfect because of a collet-not-tight incident, but the wrench worked and I don't feel like starting over.



Nut and handle are both CRS. The only stock I had big enough for the nut was 2.5" and I was too impatient to wait, so I spent a while making pretty colored chips taking it down to size. The handle is 7/8" stock turned down to 1/2" shaft, 10mm flats to match the drawbar on the PM-30, M10x1.5 thread on the end of the handle. I polished the handle down to 1200 grit before discovering that I really wanted some grip, so I knurled it, then used emory paper to knock down the sharp heads of the knurls until it was comfortable.

I know that making a ball turner and turning a ball is considered de rigour for the handle, but I like this better.

I'm very satisfied and I think it will make the lathe more usable.

I know basically nothing about conventions for making prints, so the attached PDF won't look like anything you've ever seen before, but it probably conveys the idea well enough.

Here's a model visualization (without threads):

 

[mcdanlj]

I have already made use of having multiple handle sockets in the nut to move the handle to a more convenient position for one particular operation, so I'm glad I did that. Also glad that I did them 60⁰ apart, as 90⁰ or 120⁰ would have been too much for convenience.

 

[mcdanlj]

The shallow blind sockets seemed like a good idea at the time, but were a mistake. I didn't have enough thread engagement and damaged the threads. Also, the .2" wrench flats aren't deep enough. Finally, I didn't polish the bottom, making it more likely to turn the whole QCTP instead of just locking it down against the cross slide.

I have a slightly modified design, drilling the handle sockets all the way through the body, with deeper wrench flats.

If the new design is an improvement I'll share new prints. In the meantime if anyone else is thinking of making one, let me know and I'm happy to share new prints provisionally.

 

[mcdanlj]

New QCTP top nut progress: It seems like it would be a good idea to use a needle thrust bearing under the nut to keep from turning the QCTP when tightening the nut:



I also modeled a handle. Here's a view of the assembly with the nut transparent to show bearings and bearing washers:



Here are the bearings (TC1423 or NTA-1423 equivalent) and washers I used in the model:

1. Bearing: https://www.mcmaster.com/5909K34
2. Washers: https://www.mcmaster.com/5909K47

 

[mcdanlj]

McMaster won't sell me fewer than 5 needle bearings, so I went to ebay: https://www.ebay.com/itm/NTA1423-TH...SHERS-7-8-X-1-7-16-X-5-64-BAB170/123620961767

I managed to re-discover that when you drill out through an angled wall (relative to the axis of rotation of the bit) it's really easy for the bit to grab and break, and I ended up scrapping the part I was making as a result of the broken-off bit filling the hole and sticking into the center where it would damage the tap if I ran it through. I worked out a few more things I want to change in the design while I was working on it, so not a complete waste of time. And now that I have 1 7/8" stock, less of a waste of material, too.

I put the old 1" hex nut back on while working on the new nut, and set up the washer/bearing/washer stack under it, and it does have the effect I want of making it easier to set the QCTP angle.

 

[mcdanlj]

I didn't scrap the part after all. I realized I could use a 1/8" grinding tip on the dremel to grind away the top of the drill bit, after which I was able to drift it through the rest of the way. I had mucked up the hole enough in the process that I drilled it through with the largest center drill smaller than my final size for tapping.

On to the next ops!

 

[mcdanlj]

New nut looks a lot like the old nut, but works better, so the new drawings, such as they are, are attached.

Wrench flats at least 0.3" high are the minimum I would do.

The depth of the bearing seat is critical. The washers are .032" thick, and the lower washer must be captive but protruding. If you bore the bearing seat too deep, you can turn down the outer face slightly. I got lucky; I had forgotten to print out new prints in which, based on the models from McMaster, I had made the bearing seat 0.14" deep, which would have been too much. 0.125 might be OK; 0.13 works. Placing the washer stack properly is a pain. I had to poke the lower washer with a shim until it set into place.

If I were starting over from scratch, I would consider the thicker alternative washers and making the wrench flats 0.4" tall instead of 0.3", but these prints are how I actually made it and it's working.

 

[mcdanlj]

It turns out that I made the threaded portion of the handle too long, and it mangled the thread on the rod before I figured out what was going wrong. I also didn't bore the thread relief deep enough, which makes it hard to start correctly. As long as I was tweaking things, I also made the flats 0.4" deep instead of 0.3" deep.

I have more work to do. ☹

 

[mcdanlj]

I cleaned up the threads on the rod, bored out the thread relief 0.8"ø 0.6" deep, cut the handle threaded portion to .35", and it all works a charm now. I still have the 0.3" flats rather than 0.4" flats. I would make 0.4" flats if I were starting over, but good enough is good enough; on to other projects.