Sunday, April 24, 2016

Indexing tool for watchmakers lathe

Hello friends
Today I completed the indexing tool for the watchmakers lathe. I've had on my wish list making some very fine rope knurl wheels and in order to do this I needed to be able to very accurately index the chuck. Having recently completed the new stands for the lathe with the accessory mounting t-slots, it seemed a perfect opportunity to design the indexing set up around just that. Below are the results
Watchmakers lathe indexing tool mounted and adjusted

I had used the indexing pin and holes that come stock on the back of the headstock phenolic pulley. It's very hard to get light into there to insure a visual confirmation of inserting the pin into the right hole. I designed this new unit to put the pin on the back of the indexing plate and I put the pin support arm out far enough for good light and good visual line of sight.

I designed and 3D modeled the mounting tabs that use a 1/4-20 bolt to slide into the T-slots. You can see the mounting here.
T-slot mounting for Watchmakers indexing tool

I also developed the indexing pin as a spring loaded assembly. The inside of the very end of the hollow tip is tapered so that when the pin slides home it locks in place with no play at all. The pin is shaped to fit exactly into the index holes in the spindle mounted plate. The back of the pin is also tapered to leave no play at all.
Withdrawing spring loaded indexing pin

indexing pin assembly

Indexing pin guide tip

Indexing Pin

Indexing pin parts

The arm of the assembly is quite robust to eliminate any flex. I slotted the head to be able to clamp down the pin assembly. very handy as I can leave it loose and position the arm angle correctly first, then slide the pin assembly into close contact and tighten it down.
Indexing tool swing arm

Indexing pin arm clamping head

I designed and shaped the levered nut for comfort and ease of repositioning.
Indexing tool with custom clamping nut

I'm happy with the whole assembly and especially happy that it now works as part of the new accessory mounting system.
Cheers, Kevin

Wednesday, April 30, 2014

Step #1: Imagining the WW lathe Steady rest

After weeks of creating temporary solutions for holding longer pieces of stock and after an equal number of weeks searching online for a micro-adjustable steady rest (ebay included), I came to the conclusion that the vast majority of what was available for my beautiful little WW lathe were steady rests with much more basic functionality. Additionally, the vintage steady rests were regularly selling for astronomical numbers on Ebay. I resolved to design exactly what I wanted and make it! (Below is the completed result of what began as this wish to have something better than what was available).
It is now working so well, I decided to do more than post the fun of making it. I'll be offering the main parts as a kit for anyone who is interested and I'll do my best in this blog to detail all the specific process insights I learned while making this wonderful tool .
The completed Mowrer WW lathe steady rest
All purchased and fabricated parts for the Mowrer WW lathe steady rest
It is now working so well, I decided to do more than post the fun of making it. I'll be offering the main parts on ebay as a kit for anyone who is interested.
Detailed drawings for fabricating the additional parts are included with the parts you see above.

Step #2: Designing and Modeling the Steady Rest

Preliminary design layout for Mowrer WW Steady Rest
I have a lot of experience in going from concept to prototype as I am inventor with an industrial design degree and am fully trained in drafting and modeling my designs in a 3D program, and have had many of them rapid prototyped using today's cutting edge services available online.
I had also been experimenting with making parts from bronze infused stainless steel from shapeways rapid prototyping service and had been extremely impressed with how detailed, dimensionally accurate and functionally strong the parts made from this material and process were.
Preliminary 3D design

Diving in, I developed a micro-adjuster system that was low profile and could be adjusted with finger pressure yet lock down rock solid once dialed in. I also wanted the steady rest to pivot open like on the big boy lathes for the ability to perform multiple machining operations on a part and replace it into the lathe with extreme accuracy. It's also great for multiple parts in small runs.

It was also important to me to make the design easy to finish. I love doing detail work but I don't love arduous process to get to a beautiful result. I think you'll see more of how I've developed these parts to facilitate easy lapping, filing and minimal machining with maximum accuracy as the steps proceed.

Step #3: Establishing the first surfaces on the Steady Rest frame halves

Well, Christmas in September arrived! The upper and lower parts for the frame were the first to arrive from Shapeways. As you can see, the finish resembles casting even though there is no casting involved. A big difference is that there is no differential cooling shrinkage and warping happening like you get in traditional casting. This means I didn't have to design an overly thick part to remain material safe and that in turn has huge benefits like:
  1. All critical surfaces are very close to final dimensions and can be brought to final dimension with a file and lapping, or you can machine them as well, your choice. I used both.
  2. I am able to include very accurately located guide holes for drilling out screw and pivot locations without having to blue and scribe or spend hours doing centering and numerical set up on a mill.
The raw bronze-infused stainless steel frame parts

Raw lower frame part showing guide holes on the back

Raw upper frame part
The very first surface to fit are the sides of the two little alignment nibs on the top surface of the lower frame half. This can be done with an edge file (only the edge has teeth), or by milling a very small amount of material off the mating surfaces of the top flat and the sides of the alignment nibs. Be sure to check frequently and take pains to make these surfaces generally perpendicular to the front face of the steady rest (the face without the clamp tightening screws). It's not hyper critical as the true reference surface (the front) will be lapped with both parts held together insuring alignement.
frame mating surface fitting

Step #4: Lapping the front faces on the Steady Rest frame

I was careful to keep a slight interference fit on the alignment nibs in their housing slots on the top half of the frame. I can now push them together and easily hold them in place with one hand. This is important because the next step is to lap the "front" face of both parts simultaneously on a flat surface using increasingly finer grits of sandpaper from 80 grit to 600 grit. I designed the frame to work this way on both the front and back. As I lapped, I was careful to keep changing up how I held them and keep doing circles and figure 8's on the abrasive paper so as not to lap more metal off of one side and lose parallel from front to back. This didn't take more than 20 minutes to bring up a great surface that just looks terrific. I stopped at 600 until the whole unit is built because of the scratches I'll undoubtedly get from some of the other work.
Top and Bottom frame parts lapped held together to 600 grit

Step #5: Lapping the back faces on the Steady Rest frame

Rinse and repeat for the back using a feeler gauge to keep testing that you are staying absolutely parallel to the front face. Of course, you can also use a mill to do the same now that you have a good flat front surface to set face down. As with the front, just take off enough to get to a smooth surface. I've designed it so that the front to back thickness is not critical (but parallel is key).

You'll notice I added two brass strips to the saddle surface of the bottom of the frame. You can choose not to but I've just carefully lapped a 15 inch lathe bed that took hours and hours and I want a softer metal touching it wherever I can. There's plenty of material on the raw part to tune the center height to fit any of the WW style lathes.
Back of top and bottom frames lapped

Step #6: Making and installing the pivot on the Steady Rest

With both faces as reference, I machined the mating pivot faces flat. You can use a mill or even your lathe by making a temporary jig to hold it vertical and positioning correctly on your cross slide. With that done, it's a simple matter to clamp the halves together and drill through the guide holes in the parts at the same time. This ensures absolute alignment. The dimensions for the pivot are included in the detailed part drawings included with the kit. You could make the pivot pin out of Air or Oil hardening steel but I found plain old mild steel works fine. Again, your choice. The screw is a stainless steel hex head cap screw 6-32 by .5 inch long. All the finger clamp screws are the same so that one Allen key adjusts everything.
Inserting the steel pivot pin
I've made brass fillet washers for the pivot screw and for all the finger clamp screws as well. I like the addition of the brass with the bronze/stainless color and they spread out the stresses. You can design whatever you'd like here. I chose to make the fillet washer .175 thick for easy finger access to the clamp screw to spin it on and off once its loosened.

View of the pivot pin slightly recessed from back surface with screw and fillet washer
Top securing screw and fillet washer in place

Frame top pivoted open

Indexing tool for watchmakers lathe

Hello friends Today I completed the indexing tool for the watchmakers lathe. I've had on my wish list making some very fine rope knurl ...