Tandy Stitching Pony Modification...

[Martyn]

5 hours ago, bkemp said:

Really like this modification! Thanks for sharing in detail! 

Can anyone tell me the inside measurement of 2 clamp arms or the block at the bottom on this specific pony?

I made a homemade pony and would like to add the spring. What I really need to know is how much longer the spring is than the gap between the arms. I can calculate this once I know the space. 

The gap is...

Fully closed: 56mm,  fully open: 60mm - and the inside washers (1x steel penny washer + 1x rubber penny washer) are 4mm each side. But remember, the legs on a Tandy clamp are in a state of compression, so are squeezing on the spring at all times. So the 65mm spring is about 48mm fully compressed and about 52mm with the clamp fully open. That 4mm of movement in the spring, creates about 22mm of 'range' at the jaws. The jaws will open wider than that but need a little manual assistance. I was limited because the legs of the clamp are glued in place and I didn't want to risk breaking them by trying to force in a longer spring. But if I was doing it again, I'd probably try and carefully take one of the legs off and install a 70mm spring just to give it a little more range - though I haven't actually needed more so far.

Oh and the centre line of the spring is 185mm below the very top of the jaws.

Go with the yellow 'light duty' springs. They are plenty strong enough.

 

Edited November 10, 2016 by Martyn

[bkemp]

3 hours ago, Martyn said:

The gap is...

Fully closed: 56mm,  fully open: 60mm - and the inside washers (1x steel penny washer + 1x rubber penny washer) are 4mm each side. But remember, the legs on a Tandy clamp are in a state of compression, so are squeezing on the spring at all times. So the 65mm spring is about 48mm fully compressed and about 52mm with the clamp fully open. That 4mm of movement in the spring, creates about 22mm of 'range' at the jaws. The jaws will open wider than that but need a little manual assistance. I was limited because the legs of the clamp are glued in place and I didn't want to risk breaking them by trying to force in a longer spring. But if I was doing it again, I'd probably try and carefully take one of the legs off and install a 70mm spring just to give it a little more range - though I haven't actually needed more so far.

Oh and the centre line of the spring is 185mm below the very top of the jaws.

Go with the yellow 'light duty' springs. They are plenty strong enough.

 

Thanks for getting those measurements!  Just for clarity, the gap is 60mm with no tension? If not, could you please measure the block between the arms at the bottom? That would get the measurement with no tension. 

 

The measurements on mine like it sits: 38mm no tension. 32mm closed. 

I am looking at the yellow spring that is 16x8x45mm. Thoughts? 

[Martyn]

1 hour ago, bkemp said:

Thanks for getting those measurements!  Just for clarity, the gap is 60mm with no tension?

Correct. But like I said, the Tandy pony has clamping tension in the limbs, they are not parallell and the block at the bottom is not square, but a slight wedge. If I remove all the hardware, the top of the block is 58mm and the jaws are clamped together. It's actually perfectly usable without the bolt and wingnut. If you watch this video of an unmodified Tandy Pony, you'll see what I mean:

 

1 hour ago, bkemp said:

The measurements on mine like it sits: 38mm no tension. 32mm closed. 

I am looking at the yellow spring that is 16x8x45mm. Thoughts?

Yeah, that sounds about right. You have to remember you'll add some with the washers. It also depends how far down you put the clamp, but yeas, sounds about right. It depends how wide you want the jaws to open under the force of the spring. It looks like a 45mm spring will open them to a little past neutral, but that is just an educated guess.

Edited November 10, 2016 by Martyn

[bkemp]

Ahh,  that makes sense how it can be closed and pressure applied so easily. I may be modifying my block with a wedge or take 1/2" out if it's too difficult to get it clamped. 

The clamp position is nearly identical to yours. 

Thanks again for you help! 

[Martyn]

I'd try it as-is first, you shouldn't have any problem clamping it, I think the clamps are rated for about 200lbs or something ridiculous. The cam puts a helluva lot of force through the limbs. If anything, I think yours may work better. In fact, you may not need a spring at all.

Edited November 10, 2016 by Martyn

[AndyL1]

Excellent mod! I think I found the spring on Amazon:

 

https://www.amazon.com/16mmx65mm-Chromium-Lightest-Spring-Yellow/dp/B018RSYE08/ref=sr_1_1?ie=UTF8&qid=1478827802&sr=8-1&keywords=16mm+x+8mm+x+65mm+Spiral+Chromium+Alloy+Steel+Stamping+Compression+Die+Spring

Thanks for sharing this. I already order the clamp.

[Martyn]

6 hours ago, AndyL1 said:

Excellent mod! I think I found the spring on Amazon:

Yep, that's the one I used.