New design for threading proximity sensor on PM-1340GT lathe.

[Rich V]

I wanted to install a threading proximity sensor on my PM 1340GT for a long time but procrastination being what it is I just got around to doing it. First, I wanted to use the existing micrometer stop and have the sensor easily removable for safe storage when not in use.

Second, since I have a VFD installed using the original lathe relays as outlined by Mark "mksj" I needed to find a way to integrate the sensor stop/start signal into the existing lathe setup.

First, the sensor micrometer stop design.

It is composed of two major components both made from 1/2" aluminum plate.

The mounting plate uses two 1/4 -20 socket screws to attach to the micrometer stop. Slots allow for slipping the plate over the socket heads then sliding to set proper location of the front plate.
The mounting plate has two holes drilled for shoulder screws and springs. These provide the force to return the front plate to the rear position.

The front plate houses the prox sensor and attaches via the shoulder screws. It has a slot cut to allow the face of the sensor to be recessed preventing the sensor from contacting the carriage.

The rear has a cut out for the micrometer shaft. Since the shaft sits proud of the micrometer stop face the recess allows the front plate to sit flat against the micrometer stop.

Mounted on the lathe. Note quick detach plug and panel mount attached to the head stock.

Complete unit. Removal/mounting via two socket screws and quick attach cable mount.

The way I Incorporated the sensor into the lathe control circuit was a version used by bench https://www.hobby-machinist.com/thr...-control-board-and-switches.49022/post-446310

Setup works great. Cut a 1-3/8 x 24 tpi thread in 17-4 SS @ 500 rpm to a close shoulder. Stopped +/- 0.002 on each pass.

Thanks Mark and "bench" for providing the background info to make this possible.

 

[Jason812]

I like the quick connect plug. I need to modify the one Mark made for me to keep it from just being set under the gears.

I think .002" within zero is what I get too. I learned though to calculate how far the compound will be extended and set the prox stop off the the theoretical last pass. It really changes on a 8 pitch thread.

 

[Rich V]

I like the quick connect plug. I need to modify the one Mark made for me to keep it from just being set under the gears.

I think .002" within zero is what I get too. I learned though to calculate how far the compound will be extended and set the prox stop off the the theoretical last pass. It really changes on a 8 pitch thread.

@Jason812

This is the quick connect I used.
https://www.amazon.com/dp/B08786G8SV?ref=ppx_yo2ov_dt_b_product_details&th=1

 

[B2]

The mounting plate has two holes drilled for shoulder screws and springs. These provide the force to return the front plate to the rear position.

Hi @Rich V

Nice! Thanks for posting this.

I used shoulder bolts in my design, as well, to provide guides, but no springs. I too did not want to throw out the stop I had purchased from PM. So, I use some long magnets to pull the shoulder bolts to the stop body where they slide along the magnets. Using the bolt on block with the shoulder bolts and springs is a better idea. However, more recently, in the design of a clamp mechanism for holding a digital dial gauge snug, I decided to use spring returns to keep pressure on a plate. I wound up turning a 1/4" shoulder bolt down a bit so that a 1/4" ID spring I had on hand would slide over it. However, the spring is a bit too strong. So in your nice photos it looks like the throw of the springs are considerably shorter than the screw adjustment that is available in the mechanical stop. I don't think this is a problem, but was this due to the limited operating distance of the compression springs?

Can you please provide info on the sizes of the shoulder bolts and springs as well as spring force or model numbers that you used. Finding springs to fit standard size shoulder bolts that I already had on hand was a problem.

You may have seen it, but below is the link to my solid state VFD conversion design. In the main circuit drawing you can see where the proximity sensor turns off the lathe run latch circuit. At the right hand side of the first row of the posted attachments, Part II or the Part II Fig. will show the control circuit.

VFD conversion using solid state electronic components.

PS. For a while Grainger was reducing their stock of shoulder bolts and some of them are priced very inexpensively. https://www.grainger.com/product/GRAINGER-APPROVED-Shoulder-Screw-3-8-in-Shoulder-4XY36




Dave L.

 

[Rich V]

Hi @Rich V

Nice! Thanks for posting this.

I used shoulder bolts in my design, as well, to provide guides, but no springs. I too did not want to throw out the stop I had purchased from PM. So, I use some long magnets to pull the shoulder bolts to the stop body where they slide along the magnets. Using the bolt on block with the shoulder bolts and springs is a better idea. However, more recently, in the design of a clamp mechanism for holding a digital dial gauge snug, I decided to use spring returns to keep pressure on a plate. I wound up turning a 1/4" shoulder bolt down a bit so that a 1/4" ID spring I had on hand would slide over it. However, the spring is a bit too strong. So in your nice photos it looks like the throw of the springs are considerably shorter than the screw adjustment that is available in the mechanical stop. I don't think this is a problem, but was this due to the limited operating distance of the compression springs?

Can you please provide info on the sizes of the shoulder bolts and springs as well as spring force or model numbers that you used. Finding springs to fit standard size shoulder bolts that I already had on hand was a problem.

You may have seen it, but below is the link to my solid state VFD conversion design. In the main circuit drawing you can see where the proximity sensor turns off the lathe run latch circuit. At the right hand side of the first row of the posted attachments, Part II or the Part II Fig. will show the control circuit.


PS. For a while Grainger was reducing their stock of shoulder bolts and some of them are priced very inexpensively. https://www.grainger.com/product/GRAINGER-APPROVED-Shoulder-Screw-3-8-in-Shoulder-4XY36




Dave L.

Hi Dave

These are the shoulder bolts: 91259A103 https://www.mcmaster.com/catalog/129/3478/91259A103
These are the springs: 9657K365 https://www.mcmaster.com/catalog/129/1494/9657K365

With this set of hardware I get ~0.6" of travel.