Any tips for designing a fixture plate / tooling plate?

[thackman]

I'm using a Tormach PCNC mill and most of the parts that I'm cutting these days are from 6"x8"x 1/2" 6061 plate. I've been clamping them directly to the table with a sacrificial piece underneath but it seems a bit crude and slow for runs of 5-10 parts. For the past year I've been looking for an affortable piece of tooling plate and finally found a 12"x12"x3/4" piece at the scrap yard for $10.00.

Are there any things I should consider when I'm designing this? I was planning on counterboring some holes to attach it to the table. Drilling and tapping a grid of holes 1" on center for #12-24 cap screws. Flycutting the surface. Then adding some plexiglass sides to make a mini-enclosure for cutting w/ flood cooling. I'm not sure which clamping strategy will work best yet. At first I'll either put screws through predrilled holes in the part or make some small strap clamps. Mitee-Bite hex clamps and toe clamps look interesting but are a bit pricey and they don't come it 12-24 only 10-32 and 1/4-20 which seem a bit small and a bit large respectivly. Toggle clamps seem like they might be handy if I'm doing light cuts. Overall I'm looking for a quicker, more repeatable way to hold the stock so I can mill the internal features and then cut the profile all in one setup. I've tried double sided tape but it can only withstand very light cuts and it doesn't like coolant.

I've seen some tooling plates that alternate the threaded holes w/ dowel pin holes. Some tooling plates have a grid of small coolant channels bit I don't see how they can be very effective. Are there any other features that might be usefull?

[Crevice Reamer]

Congratulations on a great find on the 12 x 12! Have you seen THIS:

http://hossmachine.info/projects_2.html#tooling%20plate

CR.

[Crevice Reamer]

Or THIS:

http://www.hossmachine.info/projects_8.html

CR.

[BobWarfield]

Haven't made a tooling plate yet, but have collected some notes here:

http://www.cnccookbook.com/MTMillFixturePlate.htm

[sansbury]

If you're just doing ordinary parts, there's no rocket science. Most people like to provide both threaded holes and plain ones for dowel pins since pins are much better for precisely locating things, especially when you have to move parts around. If the plate is aluminum, you can use bushings to line the holes for the pins so they don't wear out. If you'll only use the fixture for a few parts, don't sweat it, it will last.

The tooling plate is just a fixture used for other fixtures for specific parts. It makes it easy, for instance, to elevate a piece of bar stock above the surface so you can mill a profile without a spoilboard.

Another trick that is often useful is to program/design both the part and the fixture together. This also helps you to discover and prevent collisions and major "duh!" events before too much time and material are wasted.

Provide reference points on the fixture for re-zeroing. This way you can swap fixtures in and out and re-zero the mill quickly. You may be able to keep several different fixtures on the table at once and quickly swap between making parts on any of them this way.

K.I.S.S. Your goal is to make parts, not fixtures.

[sansbury]

Some very good and practical tips on pinning and fixturing here:
http://industrialhobbies.com/howto/p...otes_index.htm

[hoss2006]

When I was a machine shop foreman, many of the fixtures we used held
the parts down with DE-STA-CO clamps.
We used steel bumpers instead of the rubber tipped ones and they held firm even when drilling 1 in. holes.
2-4 should work.
Wholesale Tool has several sizes up to 750 lbs.
Only takes a few seconds to change parts.
They make many other types too.
Hoss

[rowbare]

This site shows a nice tooling plate build.

http://www.finelinehair.com/home/Tooling%20Plate.htm

[hoss2006]

I would probably use stock about 1 1/2 wider than the finished size.
Use locater pins on the left edge and back corner,
clamp the stock on the 2 edges supported with a couple 1/2 x 1/2 x 6 spacers.
Do the internal milling, then cut out the outer profile.
It'll leave a couple 1/2 in. pieces of scrap to save and cash in at the recycling center.
Hoss

[thackman]

Thanks for the info everyone! It looks like I'm going to be doing a lot of tapping over the christmas break.

I noticed that a lot of those plates were tapped for 3/8-16 and I was considering 1/4-20 a bit big. Is there any reason why 1/4-20 would be a bad choice? Is 3/8-16 more common for off the shelf clamping components?