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View Full Version : Suggestions for cutting an Aluminum circle



neptune769
02-16-2012, 06:20 PM
Hello Everyone,

I could use your help. I need to cut out 3 circles of 1/8" Aluminum. They are 7-1/2" diam. with a 2" hole in the center and a 4 or 6 hole bolt circle at 6-1/2". I have tried using a Scroll saw with Aluminum blades as well as other types of blades. They just snap. I'm feeding it about a 1/16" a min. (very slow). I have adjusted the tension without luck. My lathe won't swing that large. All I have at my disposal is a bench belt sander, 8" bench top drill press & Dremel tool. I can't afford to have it done. I need to come up with a way to get them cut myself. The parts are 7-1/2 square to start with. If I could figure out a way to cut the corners off I could use the belt sander to get it round. I thought about putting an end mill in the drill press and using a pin to rotate the part on. But I'm a little leery about doing that. The parts will have a 2" hole in them all said and done. I guess I could cut the corners off with a hack saw a little at a time until it is roughed out. But if someone has a better idea I'm all ears.

Thank you,
Dennis

WJHartson
02-16-2012, 06:25 PM
That is what a Pullmax or similar machine was designed to do with a circle cutter attachment. You can also do it with a rotary table on a mill. Where are you located?

The Artful Bodger
02-16-2012, 06:28 PM
Can you make a sandwich with plywood then cut them out with a router?

ammcoman2
02-16-2012, 06:36 PM
Since the material is fairly thin, I would try this approach:

a) Use double sided tape and stick the plate onto a piece of plywood about the same size.

b) Mount the plate/plywood onto your lathe's faceplate with wood screws from behind using flat head screws big enough to catch both sides of the slot, yet short enough not to touch the aluminum.

c) Trepan the OD. A parting tool may work on this diameter but you may need to make up a correct trepanning bit. Take it real easy, using the compound to advance the bit.

d) Drill/bore out the ID.

e) Use a heat gun to warm up the plate which will help with removal.

Good luck.

Geoff

The Artful Bodger
02-16-2012, 06:37 PM
The end mill in the drill press would have the danger that the chuck could drop out (if it is on a taper) sending the endmill flying, spoiling the work and maybe getting blood on the floor. However if you could arrange some sort of centre to support the end of the milling cutter that would be a lot safer.

Better still would be to get a router bit with a pilot and arrange something to support the pilot.

Then there is the issue of side loading on the drill bearings which would not be good for them.

Weston Bye
02-16-2012, 06:46 PM
I use a rotary table on the verticle mill. Just rotate the sheet of aluminum on the RT while lowering an end mill. The largest wheel far in the back and the chapter ring are approximately the size of the part described in the Original Post.
<edit> oops, went back and read the OP again - no mill or RT - sorry. But this may help others.

http://img.photobucket.com/albums/0803/Weston/PhotoA.jpg

I will be telling how to do the wheels in the Spring 2012 issue of Digital Machinist.

bobw53
02-16-2012, 06:47 PM
Chop your corners with a circular saw, and then keep taking some more corners, finish out on your belt sander. A cordless circular works really well since they don't spin near as fast the corded versions(but they work too), clamp it very well, wear some type of hearing protection, it gets loud, a perfect project for 5:30 sunday morning, if you hate your neighbors.

Don't mess with the drill press like that, I don't know you from a hole in the wall, but I still don't want to see you hurt or worse.

neptune769
02-16-2012, 07:24 PM
Thanks for the replies. As I said I didn't like the Endmill/Drill press idea. Your comments just confirm that. I would use my lathe but as I stated my lathe will not swing the part. Its only a 6". As for where I'm located, I'm in the Beaumont Texas area. About 100 miles due East of Houston. I think I will chop the corners off and sand it round.

Weston, That is a beautiful Clock.

Thanks Everyone.

Dennis

neptune769
02-16-2012, 07:31 PM
Weston,

Is that clock operational? I see no teeth. But I'm wondering if the darker dots are magnets. If so that is an interesting concept.

Dennis

Weston Bye
02-16-2012, 07:54 PM
Dennis,
Yep, magnets. No physical contact between the "gears". Operational, driven by a three-phase stepper motor, or more accurately a variable-reluctance motor. One of the coils and part of the rotor is visible to the right of the second hand.

The clock is currently being presented as a series in Digital Machinist.

neptune769
02-16-2012, 08:02 PM
Really cool. I'll have to look for that issue.

Weston Bye
02-16-2012, 08:13 PM
The first article in the clock series is out in the current issue of DM. Sorry about hijacking the thread - it was not my attention.

Back to cutting circles.:D

rohart
02-16-2012, 08:28 PM
Make a 1/2" hole in the centre, and a few small holes around the centre, but inside the 2" future centre. Make a lever that can fit the small holes without interfering with the central hole.

Make a boss with a 1/2" spigot, bolted to the cross slide, so the piece sits above centre, controlled by a long lever bolted to the small holes. You could bolt it to the top slide if you firm up the gib.

Anchor an endmill in your chuck. Start the lathe, and bring the saddle up so the endmill starts to cut, and use the lever to rotate the horizontal piece into the tool. You'll have to take four or more goes at this because the lever will not allow you more that 90 degrees of travel. Use the lever solidly but slowly.

Good luck making the 2" hole in the centre !

Bob Fisher
02-16-2012, 08:46 PM
Hey Wes, great job on the clock! I just presume that it keeps excellent time. I hope you will be displaying it at the 2012 NAMES. I've been using my machining skills, such as they are, to repair clocks and make my own tools for that work. Been toying with the idea of making my own clock from scratch. Bob F.

Mcgyver
02-16-2012, 08:49 PM
since you're talking sanding it, I'll assume .001 tolerances are not required....

layout die, scribe a circle, cut out with a jig saw (decent quality one makes it more enjoyable), fret saw if you don't have a jig saw and file to the scribed line. drill the hole ( like using a cheap brad point for thin stuff), done. This basic bench work, no fancy tools required.

Don Young
02-16-2012, 09:08 PM
Lots of good ideas suggested. You could also rotate the piece on a pin and drill lots of holes around the circle, using a drill press. Then break off the excess and finish.

Bob Fisher
02-16-2012, 09:19 PM
Any reason you cannot use a hole saw for the inner hole and finish the OD by the other methods? I don't know your requirements for finish, so that may not be satisfactory for your use. If I didn't have a lathe with enough swing, that would be my approach. Bob.A

Thruthefence
02-16-2012, 09:20 PM
do you have a router? Build a "circle cutter"

something like this, but a little more robust for aluminum.

http://www.youtube.com/watch?v=CpeedCL0QNg

fixerdave
02-16-2012, 09:58 PM
... using a Scroll saw... lathe won't swing that large... a bench belt sander, 8" bench top drill press & Dremel tool...

Me, I'd rotary table it - mostly because rotary tables are fun. But, with the tools you have, maybe...

Either via circle-cutting jig (easy to make - just an oversized board clamped/screwed on the table and a pin/screw to rotate the work on) or freehand, I'd drill nearly touching holes all the way around, both outside and inside circles (being on the right side of each line of course), then scroll the waste out (just connecting the circles - should be a lot easier on the blades), then belt-sand to the line for the outside circle (the above circle-cutting jig would work really well here - Assuming you left the center in place until this part is done - just to be clear.) and hand-file the inside. You do have files don't you? You're other option is to get or make more tools, starting with a 2" hole saw for that inside hole. Yeah, people have made hole saws (hacksaw blades screwed around wooden forms - but then you have a lathe so you could do a lot better here), no idea how well they would work. If you don't have money, I hope you have time.

http://www.busybeetools.com/product_images/77/1677/B562_zoom.jpg
With a lathe you could make a circle cutter, though 7" or so would be mildly terrifying :eek: to use even if the drillpress could turn slow enough. Might work well for the inside circle though. You could also make a sanding drum for your drillpress very easily and clean up the inside hole with that.

You have a lathe, you can do anything :)

David...

darryl
02-16-2012, 10:09 PM
You can cut the inner hole with a hole saw. Use lube, clear chips often, let the hole saw and the aluminum cool when they have heated up.

You should be able to jigsaw that out easily. If that isn't working for you, something is wrong. Wrong blade, poor jigsaw, setup isn't rigid enough. If the blade is dull, you won't get anywhere. Use a lube, which could be WD, could be a wax crayon, could be olive oil. Olive oil is kind of messy, though.

If you have a table saw, you can cut those out perfectly round. You would use a carbide blade in good shape ( I often just buy a new circular saw blade and use that on the table saw to cut aluminum) . You would make a skid, which is just a piece of fairly thin but strong sheet with a guide bar attached. The guide bar can be made of hardwood like maple. On the skid you drill a center point which is half the diameter of the finished disc away from the edge of the blade. With a pilot hole in the aluminum piece, and a piece of steel to use through that hole and into the hole in the skid, you can rotate the aluminum several times, cutting off corners in each position until you can finally rotate the disc by hand while the edge gets trimmed all around by the blade. Rounds come out beautifully- round.

If you cut the center hole out first, you would need to machine up a close fitting plug for that, so you have a small enough center hole to use as your pivot point for the table sawing operation. Doing it this way will ensure that your outer diameter is concentric with the center hole.

Aluminum chips will be very sharp and probably hot, so take care. When you are sawing all the corners off, it would be good to use some means of securing the aluminum plate to the skid for each cut. If the blade catches it and it begins to rotate, it's going to become a high speed discus with no regard for human life.

In my shop, I'd have one done in the time it took me to type this. I already have a skid though- I can just put it on the saw, drill the pilot hole the right distance from the saw blade, pop the pivot pin in place, add a few hold-down screws with washers, and go.

darryl
02-16-2012, 11:32 PM
You still could use the lathe. Remove the compound, etc, to get down to the carriage top surface. Build up a table onto that to support the aluminum blank. This would be horizontal, and at a height which puts the surface of the aluminum within reach of a tool you mount in the chuck. Running the carriage left or right gives you the radius of the circle, and you would lock the carriage at that position. You will need a way to rotate the blank, so if you could make it like a rotary table, that would work. Or just mount the rotary table in place of the compound.

An adjustable boring head mounted in the chuck gives you a way to move the cutter into the plate a little at a time. The setup would look like a set of bevel gears- the small gear is the boring head, while the larger gear is the aluminum plate.

Maybe this is a bit of a stretch, but it would work.

bborr01
02-17-2012, 12:56 AM
Neptune,

Did I read that right? 1/16 inch per minute? Are you sure you don't have the blade in backwards?

Brian

Paul Alciatore
02-17-2012, 01:54 AM
Thanks for the replies. As I said I didn't like the Endmill/Drill press idea. Your comments just confirm that. I would use my lathe but as I stated my lathe will not swing the part. Its only a 6". As for where I'm located, I'm in the Beaumont Texas area. About 100 miles due East of Houston. I think I will chop the corners off and sand it round.

Weston, That is a beautiful Clock.

Thanks Everyone.

Dennis

Beaumont, TX you say. Well I am too, neighbor.

My shop is still in storage (in Silsbee) or I would do it for you. You say you have a scroll saw and that should do it. You need a fine tooth blade, at least 18 TPI, better yet 24 to 32 TPI or it will jam and break. You need at least two teeth in contact with the cut at all times. I would also use some WD-40 for cutting fluid. The aluminum may be gummy, depending on the alloy and the WD-40 will keep the blade from sticking to it and the aluminum form sticking to the teeth of the blade.

You need a hole circle so I would do them first and use them to make a sandwich of all three blanks. That will make it thicker and also help prevent binding and breaking. But do use the WD-40: it is magic for cutting aluminum. Keep it wet as you cut.

Bazz
02-17-2012, 07:32 AM
Turn it on your lathe,

Steady rest at the end of the bed make a shaft long enough to pass the bed ,sandwich the with plywood and turn with boring bar or hand tool like a wood lathe made with a old file

wood lathe can turn on the back of the headstock you could to with minimum set up time cut with hand held tool with a improvise tool rest

Bazz