Dang Dogs

[macbruce]

Anyone have any info on the do's and dont's of making your own platen table dogs? My table has 1 3/4'' holes and I went to alotta trouble to get 1 11/16'' cold rolled to make the dogs...About half the time when I go to seat the buggars they pop up no matter how big the sledge is or how hard I bash em. The other thing the raise little humps in the surface that eventually break off.....Angle wrong? Do they need to be thinner at the bend? Material too big???...Thanks in advance....mb

[Thomas Dean]

I would think the angle is off, and/or too close to the work. I have never had the pleasure of owning a platen table but use a hold down like the for a lot of my work, both real job and at home. My hold downs are longer and don't fit the hole that tight. With you material size the is only 1/32" clearance to the sides, I think more is needed to 'bite' the bar better. Maybe some 1 5/8" or 1 9/16" would work better...

[John B]

IMHO The angle is off due to the too close fit, you need some clearance to benefit from the "wedge" effect, and how thick is your table?

The depth of holes in relationship to the length between the top contact area and the lower contact area will affect the gripping power, and will determine the size of bar required,

The bumps are probably due to excessive pressure in a concentrated area created by trying to force your existing dog into the holes to get it to clamp securely.

[bajajoaquin]

My only experience is with a smaller scale, having made exactly one anvil hold-down that fits in my pritchel hole.

However, one of the things that was stressed when discussing its making was that you needed some spring in the design. I'd say that you want to have the "arm" that holds the work piece be longer, with more of a curve to it. I think your current parts are too rigid. The platen hold-downs that I have seen have followed that design.

[John B]

My only experience is with a smaller scale, having made exactly one anvil hold-down that fits in my pritchel hole.

However, one of the things that was stressed when discussing its making was that you needed some spring in the design. I'd say that you want to have the "arm" that holds the work piece be longer, with more of a curve to it. I think your current parts are too rigid. The platen hold-downs that I have seen have followed that design.

Yes I would agree with that, I omitted to say the arm should be drawn down much thinner with a curve and a foot pad on the end to give the whole thing some "give" to allow it to grip the work.
Apologies for the omission

[macbruce]

Thanks all, we seem to have fixed it.......Not wanting to scrap my expensive CR 1 11/16'' which I agree is too fat, I decided to have a go at forging the bend point making it less stuborn to flex. Kept the same angle and put a foot on it..... I left the foot off because I saw some shopbuilt dogs at Flagstaff in 2000 that seemed to work fine, I made what thought were copies but the arms were too short to flex properly. Getting in close with shorter dogs has advantages ......Now a 4lb hammer cleats em with ease every time, now to fix 5 more and make some longer ones of 1 1/2'' HR, does it ever end.............

[Glenn]

I have a photo of factory built dogs in the "it followed me home" thread. You should be able to get some idea of dimensions from the photo. There is indeed a foot on the end to set against the work.

One of the things I found useful are pieces of pipe with couplings that drop into and hang on the edge of the acorn holes. These act as fulcrums for bending, or for positioning your work. If you do heavy bending, solid stock is suggested.