Holddowns for flat sheets. How to do?

[ilya]

I need an advice on how to hold down the flat aluminum sheets. My table is build from 80/20 extrusion, so it has some T-Slots in there.

I need to fix the sheets so I can flycut them and not crash in the fixture somehow. I'd like to stay away from adhesives and tapes for now, so only mechanical holddown techniques if possible please.

How would you guys approach this?

Thanks!

[multiplex]

vacuum table!

seems that 90% of the things i do on my table require vacuum hold down. I typically make a fixture for each part as they usually have some sort of special requirement that would make a generic vacuum table difficult to use.

Of course, the problem is drilling holes through your workpiece isn't acceptable

[ilya]

Well, I thought about vacuum table and it's not an option for me. Not until I move the whole CNC thing out of my place. Otherwise my wife will do something like that:

[analogman]

How big are these sheets? Thickness? Are you going to flycut the whole surface?

[ilya]

The sheets are 19" long, width may be from 1.75" to 7", but mostly 3.5". Thickness is 4-5mm (0.157"-0.197").
Yeah, I need to flycut the whole surface of the sheet.
I saw some clamps here: http://actmachines.com/cart/products.php?id=87 but I'm not sure they'll work with my t-slots though

[analogman]

I would find using fixtures in your T slots a pain, because I would have to move the fixtures to finish the job. With that thin of a material I would be concerned I was not getting the flatness I wanted when I moved a fixture.

The two options I would use you have already ruled out. Vacuum clamp would work very well for this purpose as you are not cutting through. Unlike you imply, not all vacuum systems are noisy - good ones are way less noisy that a router.

The other option is double sided tape. I use this a lot with routing/drilling .080 5052 aluminum sheet. I use the 3M industrial brand. First I lay down an MDF spoil board and mill it flat. In your case, I would use HDPE as you are not drilling through.

[ilya]

Analogman,

I'm ruling out vacuum not because of the noise, but because of the space. All vacuum generators are quite bulky, however if you know about a compact vacuum generator I'm all ears!
Please, tell me more about the tape! Initially, I've heard that it's a pain to remove it. How do you deal with that? Can you give me the exact name of the tape you use?

Something that I was thinking about is some sore of fixtures that hold the sheet from the sides, not from the top. What do you think?

[analogman]

The 3M tape I use is #9579. Hi tack, but pulls off aluminum fine. When I use with MDF spoilboard, it tends to pull up the top layer of the mdf, but for me, that is OK, because it is a spoil board. For you I would put down an HDPE or some plastic type of spoil board. Gently use a putty knife to pull up the work off the spoil board. You can get the 3M tape at any industrial supply. McMaster Carr will have it.

The vacuum system I use is quite small - about the size of a bread box. Got it from veneer supplies. Its the excel 1. http://www.veneersupplies.com/produc...roducts_id=248

I am really a big fan of vacuum - if I can use it. Unfortunately a lot of my work has cut through, and are small runs. That makes it a challenge for vacuum.

[Regnar]

I cannot say how well this will work for flycutting but you might want to look into a product called gravogrip. We use this for cutting out small signs. I uses a static type of cling to hold the pieces.

[Drools]

I have a small 24" x 40" 80/20 gantry router and I think I'm going to try something along these lines. I have 5 pieces of T-track 3/8x3/4" which I will space out between pieces of HDPE or UHMW plastic. I was just given 2 pieces of 1/2" thick by 16" wide by 10' long UHMW plastic that I would like to cut into strips if I can figure out how, SAFELY! The plastic will sit 1/8" above the T-track which gives me a small margin of error if I cut into the spoil board. I want to embed some threaded inserts into the plastic, ones like these. Any thoughts?

[Grunblau]

The 3M tape I use is #9579. Hi tack, but pulls off aluminum fine. When I use with MDF spoilboard, it tends to pull up the top layer of the mdf, but for me, that is OK, because it is a spoil board. For you I would put down an HDPE or some plastic type of spoil board. Gently use a putty knife to pull up the work off the spoil board. You can get the 3M tape at any industrial supply. McMaster Carr will have it.

I use Shurtape Indoor/Oudoor Carpet tape #DF 550. I have tried many other tapes with mixed results but the Shurtape is by far the best. I mill through it and have had no issues removing it from MDF or wood. Only available at Lowe's. Don't bother going to the Home Depot.

[morphious69]

there is a sort of wax too that is used for milling. wholesale tool used to carry it but sadly they stopped before I could test it out or buy some stock for later use. Supposed to be usable on a mill for cutting steel parts then you use a heat gun or some such to remove it from the fixture you are holding the part on. on aluminum I would think that product (if it performed like they were saying) would be perfect.