Clutch / Shear pin for Smithy Midas ?

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heavyg603
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Clutch / Shear pin for Smithy Midas ?

Postby heavyg603 » Sat Aug 26, 2017 10:36 pm

So I've had a few unfortunate crashes (both the headstock and a dig in) on my Midas 1220 LTD. Was toying with the idea of trying to build a clutch or at the very least put shear pin(s) in on the feed shaft vs the solid ones in there now so I'm doing a little less swearing and replacing gears. Has anyone done something like this ?

spro
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Re: Clutch / Shear pin for Smithy Midas ?

Postby spro » Sun Aug 27, 2017 12:28 pm

I did something like that but the results were not the best. All brass is not the same and can become "slightly sheared" over use. This exhibits when things don't quite line up. When a pin or key is "slightly sheared", it is a bugger to get out. The pin/key metal ( in my humble case) smears across the surface and locks between the two elements. This is particularly noticeable with smaller vertical engines. You have a heavy flywheel at the top and the other side a blade which hits a brick. Something has to give before bending the crankshaft. Everybody knows this, so what.
"What" is that key which is partially sheared and just gets worse. That throws the timing off and engines smoke, don't start etc.
So I follow you and this is a good question. The pin should break at certain impact but there should be many in reserve. I was almost thinking ceramic but that is nuts. Almost, almost seems like Bakelite.

spro
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Re: Clutch / Shear pin for Smithy Midas ?

Postby spro » Sun Aug 27, 2017 5:53 pm

With a lathe, it can't be on the verge of breaking and screw things up. That means the joint must be accessible. Wait a freakin decades.. They had clutches on the older copy machines. That's right, centrifugal and machines jammed all the time but didn't foul the workings. I hadn't thought about those in years. In some technical manual of a larger Xerox, there was adjustment and kept a few parts. After that, it was timed and early steppers.

Torch
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Re: Clutch / Shear pin for Smithy Midas ?

Postby Torch » Sun Aug 27, 2017 6:46 pm

I put shear pins on after a couple of, um, learning opportunities. I replaced the pin for the feed screw with a brass dowel and I made brass keys for the change gears.

I also learned not to crash, so I really haven't tested them thoroughly. But they haven't caused me any problems.

heavyg603
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Re: Clutch / Shear pin for Smithy Midas ?

Postby heavyg603 » Sun Aug 27, 2017 7:38 pm

I thought about making some brass pins since the clutch seems way too complex on the cross feed. I hear everyone on the "crash less" idea, and I do now but the last one was a bigy and ripped out a fixed shaft in the gear box and it happened in a split second after a tool just dug in unexpectedly. Just trying do some risk management.

There is also a design flaw in the mounting on this machine that reduces the travel by an inch or so on the carriage, this seems to nearly bite me in the butt a few times since its in an odd place.

heavyg603
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Re: Clutch / Shear pin for Smithy Midas ?

Postby heavyg603 » Mon Aug 28, 2017 3:28 pm

Torch wrote:I put shear pins on after a couple of, um, learning opportunities. I replaced the pin for the feed screw with a brass dowel and I made brass keys for the change gears.

I also learned not to crash, so I really haven't tested them thoroughly. But they haven't caused me any problems.


Have the shear pins gotten any use ?

Torch
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Re: Clutch / Shear pin for Smithy Midas ?

Postby Torch » Mon Aug 28, 2017 8:03 pm

I was about to say no, as I have managed to avoid crashing since. But then I remembered that my son managed to shear one (the feed screw dowel, IIRC) as part of his learning process.

toddalin
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Re: Clutch / Shear pin for Smithy Midas ?

Postby toddalin » Tue Aug 29, 2017 1:03 pm

On a related note, The first time my table went beyond it's limits using the lathe with the power feed, it snapped the spline shaft. The table is marked 5-1/2" in each direction from the center and it snapped the shaft at under 5" in one direction. (The other direction goes over 6" from the designated center.)

I was able to get a replacement spline shaft from Smithy, and actually bought three just to get one that fit properly (typical Chinese). Then I used the mill to trim it to the right length.

THEN, I added a contactor and a reed switch in both the X and X directions on the table. I put magnets on the chassis and they will disengage the contactor just before the table crashes.

heavyg603
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Re: Clutch / Shear pin for Smithy Midas ?

Postby heavyg603 » Tue Aug 29, 2017 8:15 pm

toddalin wrote:On a related note, The first time my table went beyond it's limits using the lathe with the power feed, it snapped the spline shaft. The table is marked 5-1/2" in each direction from the center and it snapped the shaft at under 5" in one direction. (The other direction goes over 6" from the designated center.)

I was able to get a replacement spline shaft from Smithy, and actually bought three just to get one that fit properly (typical Chinese). Then I used the mill to trim it to the right length.

THEN, I added a contactor and a reed switch in both the X and X directions on the table. I put magnets on the chassis and they will disengage the contactor just before the table crashes.


This sounds exactly what I'm looking for do you have any pics of the setup ? I'm a little unclear of what you are disengaging with the switches, the whole motor or is there something else to kick out the feed lever ?

toddalin
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Re: Clutch / Shear pin for Smithy Midas ?

Postby toddalin » Wed Aug 30, 2017 1:39 pm

I use a 50 amp Gould 2200 contactor, located inside the machine, that has its armature wired to the wall outlet before the power reaches the on/off switches for the mill and the lathe (separate switches on separate motors). So if the contactor is open, no power reaches the machine motors.

The added advantage (YUGE!!!) is that I can turn on the more delicate machine switches before applying power to them and turn them off after the power is removed. This prevents them from arcing and burning out, as Chinese switches WILL EVENTUALLY DO! (Mine was just starting to falter.)

The contactor needs 12 volts to trigger, and I also put a 12 volt wall wart in the machine. An added switch turns on the wart that sends 12 volts to the contactor through the normally closed arm of a small 12 volt relay. It also sends 12 volts to the two reed switches attached to the table. Four magnets (2 for X and 2 for Y) placed along the chassis will close the reed switches sending 12 volts to the small relay making it open its normally closed arm that sends power to the contactor.

This could also be done without the small 12 volt relay by using normally closed reed switches that will just open the power from the wart to the contactor, but these reed switches are a bit harder to come by and I had the others, and 12 volt relay, on hand.


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