Milling AL flat on a piece that's too large for a vice.

[Cartierusm]

SO i've got some 6061 3/8" x 3 1/2" x 9 1/4" aluminum and I need to make it flat and relatively parrallel to each side. Now My Kurt vice has a 6" width capacity as I have a permanent stop block on one end for aligning parts. So that mean 3 1/4" is hanging off one side of the vice. I decided to just make a large jig out of 3 1/2" x 2" x 10" aluminum block. I will mill this flat and parallel and then use it as my jig to CNC machine the rest of the 3/8" flat bar. The problem is how do I get one side flat first, becasue if I bolt this to the jig first it will pull the bow out of it, but then it'll come back the minute I take it off the jig? I can't mill it flat with out the jig or it will vibrate and bounce as the cutter is moving over it, already tried it today with some wood as a brace on the other end.

Any suggestions?

[Geof]

Make yourself a set of custom jaws for the Kurt long enough to hold the full length?

Alternatively; mill a 3/8" deep slot in your big block and tap 1/4" holes along one side. Actually make the slot about 4" wide and then use setscrews to hold the parts for the first facing with a length of cold rolled between the screws and the part.

[PixMan]

With a 6" wide vise you should only have 1-5/8" sticking out from either end of the vise jaws. Lose the vise-mounted stop and make up a quick & easy table-mounted one, and center the stock. I thought everyone made one of those as their first trade school milling project!

Now with a more rigid set-up...If you have a good, free-cutting face mill this should be rigid enough to mill without any issues at all. What are you using for a tool right now?

[mactec54]

Hi Cartierusm

You can also put your Kurt vice jaw on the back of the moving jaw & on the front of the fixed jaw for holding longer parts

[Cartierusm]

Thanks for the suggestions. I need the table space for other things such as my 4th axis. I forgot about the outside kurt jaws. I'm using a 2" face mill with inserts, no I don't have the AL ones, but I've looked, it's going to be bead blasted and then anodized so a matte finish is fine.

[Gerardo1]

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[Cartierusm]

Ok so clamping this thin piece of AL long ways didn't work as it bowed with even a little tightness on the vice. I ended up using a piece of thick AL stock under in ontop of parallels and that kind of worked. Not flat enough but good enough for testing.

So a couple of questions will regular flat bar 3/8" x 3 1/2" milled down to .345" ever be relatively flat. I mean maybe this is a beast that can't be tamed, will it always kind of bow becuase it's so thin and hasn't been streesed relieved? If the answer is no, that it can be flat for the most part, can AL be surface ground? I've never used a surface grinder so I'm not sure if aluminum can be ground on it.

Next how hard is it to setup up two Kurt vices in a row to use as one big vice? I was thinking if put a thick ground stock in one aligned it and then tightened the stock in that then clamped the jaws of the other one on it and then bolted it down and then check it with a dial test indicator, then it wouldn't be so hard?

[Superman]

Look-up about vacuum plates

Make your own
A large Al plate bolted to the table, a soft foam type O'ring inside your finished plate dimensions, a series of grid-lines inside this O'ring to assist speading the vacuum, vacuum pump and line attached to the plate breaking into one of the grid-lines inside the O'ring
After you bolt it to the table , face it, it is now flat to any facing operation you do on the part.

[Cartierusm]

I build vacuum fixtures all the time but if the piece is already a little bowed then the vacuum would straighten it out until the vacuum is released then it would bow back.

[Glacern]

I like Geof's suggestion. Make a pair of 9.25" wide soft-jaw plates.

Get two pieces of 1x2 stock, 9.25" long each. Steel is preferable, but aluminum should be fine for this project. Drill holes for the 1/2" screws and replace the hardened jaw plates. You can either counterbore the holes and use the existing socket-head cap screws, or just get some longer 1/2"-13 screws (any type will work) and forget about counterboring altogether.

Clamp a 1-2-3 block in between the jaws and mill a step into each jaw. Now you're ready to clamp your workpiece along its entire length. Flattening 3/8" thick 6061 is definitely feasible using this method.

Multiple vises would be good for longer projects, but standard vises will still leave unsupported gaps unless you have a vise with flat ground sides as shown below.

-Sol
Glacern Machine Tools
glacern.com

[crabbass]

Using multiple vices in alignment has been common at all shops that I have been to. If your facing tool is chattering, do you have wiper inserts? If so, ditch the wipers, face with a sharper tool, positive lead, of smaller diameter and multiple passes. If you want to use the large facemill with wipers for speed and economy, your part needs axial support. If you mill soft jaws leave alot of material under the part. I think you were on the right track with the large block of Aluminum. Mitee Bite sells alot of different cam clamps and fixturing accessories for low profile clamping. If you don't have the time or funds for the fancy fixture clamps, improvise with set screws and dowell pins. Similar to what Geof was saying about clamping from the side while the bottom of the part is supported (not smashed flat).

Nice Vices Glacerne !

[DMF_TomB]

sometime long and thin plates when you tap it down on parallels you are actually bending it flat but it will spring back when unclamped.

some people try adhesive to a thicker plate. For example there are sticky waxes that will glue things together but the glue bond can be broken by reheating and or dissolve the glue in solvent like alcohol. Often this is used for holding glass lenses so they can be ground and polished to shape.

you want to glue together similar metals. For example I once used a hot melt glue gun to stick aluminum to steel once. It seemed very strong even when the plates were still a little warm. I cooled it in cold water. The plates fell apart. The difference in expansion of the 2 metals broke the glue bond.

Obviously when machining you need to also watch the plates do not get so hot that the adhesive melts and the glue bond fails.