[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]

HI I 'm BERY NEW ON CNC zone and I BIGAING TO LEARN MILL CNC PROGRAMIN I GLAD TO BE HIRE TANK YOU CNC zone

[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.

[machine_nut]

You haven't mentioned what tolerances you have and have you thought of using Jig Plate?
This is generally pretty flat to begin with and might save you some head aches.

[mactec54]

Hi Cartierusm

It can be quite a job to get the parts not to be bowed sometimes I found cast plate a little better to keep flat than flat bar

I have seen Aluminum parts/sheet Blancher ground

If you could not do it in your vice you will have to make some jaws for the vice as other posts have said

Holding the piece between the new jaws Take a light cut on the side that is bowed up do not beat it down into the vice just place it in the jaws with hand pressure on it take a light cut to clean it up do all your pieces this way turn them over then & do the other side you may need to do this with only 1 insert in your cutter or a flycutter if your cutter is beating on the part instead of cutting like butter you will be putting stress into your parts & they will bow for ever if this is the case

Once you have cut the back side turn it over & cut the other side again you will get straight flat pieces you must do even depths of cuts on each side as well

A photo of a piece I make in one Kurt Vice with long Jaws & is over 12" long & less than .250 thick

They are straight & flat with in .0002 to .0005 over the whole length

[Mcgyver]

So a couple of questions will regular flat bar 3/8" x 3 1/2" milled down to .345" ever be relatively flat

what's flat? a thou, a tenth, 1/16, ? knowing what you want to accomplish will drive the technique...but regardless thin pieces can be very difficult because they will move as material is removed

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.

this is a problem clamping any workpiece, direct to the table, mag chuck on the surface grinder, vise, whatever...they all impose force that will distort the work. its often not an issue its because the amount of distortion on a particular job/setup/shape of peice isn't enough to notice or take things out of spec....but that distortion from camping force is still there.

getting things really flat is not trivial. ignoring the material change in shape as stress equilibriums are changed, three techniques i'm aware of to get things flat are:

1 scraping one surface (quickest and easiest imo)
2 map the surface with an indicator and shim such that the surface is the same as the map after clamping; in other words create and verify a setup where the clamping is not distorting it (this is the most common way to get thin things flat on a surface grinder)
3 cast a surface for it to sit on; ie set it in something like bondo (with a realease agent) such that its current bowed shape is supported against clamping forces

[Geof]

It will move back and forth as material is removed from each side. In my experience the best approach is mill one edge smooth taking off the minimum material then hold it in a fixture as I described many posts backs; don't hold it down just lay it in the groove and clamp with the setscrews and cold rolled bare against the un-milled edge. Take a light cut, flip end for end and take another light cut; these cuts do not even have to clean up the pre-existing distortion or any subsequent distortion, just get within the tolerance of cleaning up. With luck eventually it will be flat to within 0.001" or maybe better, or worse if luck is not smiling.

[rwexec]

If the cutting pressure is not to great, carpet tape will work.
Cheers

[Cartierusm]

WOW, thanks for all the GOOD suggestions. Right now I'm using a 2" face mill with APKT 5/8" inserts that are definately for steel. I'll have to find some for AL. I think I'll work at making longer jaws and or the set screw method.

I know about Jig Plate material, is cast aluminum the same? Also where online can I find Jig Plate Material, I've never been able to find it in an easy to order online type of place. Thanks.

[Delw]

Maybe I am missing something, but geof's way is right on the money, been doing it for years on 1/4" plates milling down to .200 thickness 3.5" wide up to 16 inch's long.

your bowing could be coming from 2 things which are most common
you tightened the vise way way to tight or your face cutter don't have good alumin inserts, more than like its the latter. I use a 3" face mill

My 40x20 has 4 kurts on it with 8" alum jaws .if you cant use alum jaws cause you don't have them then your standard hard jaws will work fine. to use multiple vises with hard jaw you need to have long piece of ground stock. I use a 4" wide x 2" thick piece
clamp the bar in the vise's then put one bolt on one side of one vise and snug it indicate it in and tighten the others now everything is aligned. remember the vise jaws will only be aligned as good as your ground bar is.

one thing I will say using the back jaw and the top of the non moving part of the vise wont work reason being is your bar stock is bowed to begin with so the pressure of the face cutter will push it down usually in the middle.

. if you need to hold a tight tol. cut one side then flip it around and cut the other. but do it with parrells or cut alum jaws. I found it best that a .750 wide cut locating face on each jaw.

if your still having problems with bowing its due to your face cutter and you may have to get a fly cutter and put a 3/8's square ccmt lathe tool in it .015 rad works best for a nice finish ( thats what fits in my fly cutter).

Again the right tools for the right job come into play ( correct inserts) on thin wide parts( the parts you are talking about are not thin but the basic principle still applies

[rwexec]

There's more than one way to sink a ship.
:cheers: