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steve-ma
12-26-2009, 12:27 PM
Guys I have a 1" thich iron plate, about 12 x 14 in. It was used as a DP table 'cover'. That is, it was on the table of an old DP, acting as a fixture holder. It has a few holes in it, but nothing too bad.

What would really be useful would be a T-slot plate on the table of this DP. Do you think that this piece of iron I have is too thin to cut some T-slots in? (I have access to a Bridgeport) What size slots should I make?.... Thanks Steve

Boucher
12-26-2009, 01:03 PM
This doesn't answer the question that you ask but I will throw it out anyway. Some tapped holes would work well and would be a lot less work.

Paul Alciatore
12-26-2009, 01:05 PM
Just a seat of the pants estimate, but I wouldn't do any Tee slots larger than 3/8" on that plate. Even that may be too much if it is self supporting. With minimum depth, a 1/2" slot would be about 0.67" deep which would leave only 0.33" under it for strength. A minimum depth 3/8" slot could leave 0.5" of metal below for a lot more strength. Depends on what you are going to use it for and how it will be supported.

You might want to consider just drilling and tapping some holes for studs. Here you could easily go up to 1/2" stud size or even larger without weakening the plate. I did a smaller one (10" X 6" X 3/4") with alternate holes on a 1" grid (diamond pattern) and it worked out just fine for almost everything I wanted to clamp to it. I used 3/8" stud size as that was the only clamp set I had at the time. I did the tapping by hand, but a tapping head would make short work of it.

In some ways tapped holes are easier to use than Tee slots as you don't have to jockey the nuts into place and you can easily add a stud between two that are already in place.

Circlip
12-26-2009, 01:52 PM
3 - 0 for tapped holes Steve-ma How thick is your Bridgeport T-Slotted table??

Regards Ian.

Walter
12-26-2009, 02:11 PM
I'll also go for the tapped holes. T slots are nice at times but not always as functional as the holes. and the holes allow for some really nice adaptations to workholding. I'll try Monday to snag some pictures of a neat little fixture we use for nail marking prototype blades (one offs) it's simple, fast, and adaptable for almost anything we can come up with. It's in my to do list to make some really nice tooling plates as the ones were using now are just mild steel and quickly fashioned to allow us to complete what needed to be done. I've got a nice chunk of D2 @ 1"x4"x3'+ that will get cut into at least 2, 6" tooling plates. I use 1144 for most of my clamps and hold downs and then just harden them with the torch.

Forrest Addy
12-26-2009, 02:30 PM
If I was to suggest a rule of thumb for plate thickness to T slot depth. I think maybe 2 1/2 times the total T-slot depth would be a good figure. Another point is do the slots first then machine the plate's thickness. Milling the slots will distort the plate convex across the run of the slots. By the time you're done the plate would finish about 7/8" thick.

In other words your plate is too thin for all but the smallest standard T slot. An array of tapped holes would probably work better considering the plate's overall rigidity and distortion. You could take the smallest standard T slot (1/4) or proportion it smaller as #10 machine screw thread or maybe 5 MM metric. Just a thought.

Regardless I suggest you stress releve the plate first. A home barbecue is a great resource for stress relieving. Bury the plate in a thick bed of hot coals and ash and let them burn down to nothing for a day. The plate doesn't have to get red hot. 1200 F or so is plenty followed by gradual cooling to 200 F.

steve-ma
12-26-2009, 04:22 PM
OK, my gut was it's too thin. I will do holes. I have the 'production' table on an old Delta drill press, and if you are familar with these, it's flat and smooth. The table would have to be drilled and tapped for this plate. But with holes in this plate. at lesat I'll have some anchor points. Thanks for your advice all.

Mark McGrath
12-26-2009, 04:25 PM
Some one in the USA is selling smallish tee slotted plates on Ebay.uk.Might be suitable for bolting over your existing table.
Mark.

Walter
12-29-2009, 12:13 AM
I realize that this isn't what you had in mind, but it kinda shows the versatility of the tapped plate concept. This was made so we could pop a prototype knife blade on the vert mill and quickly gash in a nail mark. Usually we make a templated holder to do this on the horizontal mill. Time saved by going this route, hours. Some of the rounds are relieved to work as clamps.

http://pic100.picturetrail.com:80/VOL1167/4323122/22626082/380306922.jpg

http://pic100.picturetrail.com:80/VOL1167/4323122/22626082/380306920.jpg

http://pic100.picturetrail.com:80/VOL1167/4323122/22626082/380306915.jpg

http://pic100.picturetrail.com:80/VOL1167/4323122/22626082/380306910.jpg