I just purchased an off brand platen table with 1 1/2" holes and was wondering if anyone has some ideas for clamping? There seem to be plenty  of clamps for the Acorn style 1 3/4" but have yet to come across ones to fit mine. Any pics would be appreciated if you fabricated your own. So far, the quickest solution I could come up with is using the "Pony" style pipe clamps or forging the hammer in hold down types. Thanks in advance. 

The "Bessey" type clamps, usually have the bushing pinned on the end of the upright.

It would seem a simple matter to change out the bushing, ... or turn it down.

 

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Stronghand's version of the Bessey clamps have a retainer clip on the end that you just push on and can slide the screw part off.  Perhaps you could make a swage for that cross section and figure out something like a "T-bolt" that works for your platten. Maybe a wedge lock could work?

Greetings Dognose, 

Time for ol Jim to chime in.  A simple solution to lock in the uprights for use with a pony clamp.. Just pop them in the hole a sharp pull upward .. Slide the square tube down and insert the lock pin .. 

Forge on and make beautiful things

Jim

Another standard is the good old hold fast made to scale and long enough you can knock them free from underneath.

Frosty The Lucky.

Not exactly clamping but I remember a post a few years ago on the NWBA forum where they talked about using cheap tubing expanders for locking things in the square holes in a platen table. I looked around and the thread was titled "Platen table tricks" http://blacksmith.org/forum/tools-trade/platen-table-trick/

You can also steal the old dogs and wedges idea used on wood working benches. You'd just need two drop in dogs ( I'd probably make them from heavy 1 1/2" tube with a heavy plate on top to wedge against and keep it from dropping thru, and some sort of wedge to drive to lock things together.

 

The other thing I've seen done is to use the same basic idea of those milling machine clamp sets. This works best where you can still reach under and position a plate with nut, or threaded plate to take all thread or a bolt to secure the clamping bars to the work and steps. I have seen "toggles" done like Jim shows made with heavy all thread and a swing plate at the bottom.

Make a set of gooseneck hold downs. they will do for 99% of your clamping needs.

Google "goose neck hold downs" for a picture and description. 

 or forging the hammer in hold down types. Thanks in advance. 

Sounds like this is the consensus, and what I'd suggest as well.