Face Milling Question

[HackMax]

Hello folks. I can't seem to find exactly what I'm looking for as far as preparing aluminum for chrome plating by searching the net so I will put the question to you.

I have a 5" x 9" x .625" piece of 6061 and on the one side I need to take all the extrusion marks out of it so it is flat for the chrome plating. I would like the surface as smooth as possible so I would have less work preparing it for the chrome. I have a Grizzly X3 conversion and I first tried a 3" carbide indexable mill and I soon found out how important tramming the mill is as it left a small ridge in the middle on the second pass. Even if the ridge wasn't there the surface it left was still inadequate for final preparation. I plan to sand down the final machine marks with 400, 600, 1000 grit sandpapers and then buff it so no marks show in the chrome.

I thought I may be using the wrong tool so I tried a fly cutter with a carbide tool bit extended just a bit over 2.5" to cut it in one pass. The surface still was too rough for the first sanding. I've ordered an extra long square tool bit for the fly cutter so I can experiment with different cutter shapes and also help balance out the fly cutter for less vibration. I've tried different speeds and feeds but I'm not sure what would be optimum for either of these tools. It didn't seem to make a difference in the surface.

Anyone out there have any ideas or thoughts on the best way to do this and get a half decent surface. What would the best tool bit shape be for the fly cutter. I've since trammed the mill and now the dial gauge doesn't move a lick in the rotation so I can try cutting in 2 or more passes again. I have already milled the piece I started way out of spec so it is pretty much trash for the project. I will use it as a practice piece.

Thanks,

Rick

[LeeWay]

I think your key will be to use a very sharp flycutter and very slow feed and shallow DOC at least on the final pass. Use your highest spindle speed possible. Make several passes rather than just two. Say 10 passes. I think this might give you the best surface and least amount of cleanup.

I have never chromed anything, but have polished lots of aluminum. I find a random orbital sander the best for finishing out a rough surface in graduated grits. You should see a near polished like effect with the last and highest grits.
Chrome is pretty unforgiving on anything but a perfect surface.

[HackMax]

Originally Posted by LeeWay Use your highest spindle speed possible.

Yeah I couldn't get it much higher than a few hundred RPM because the bit extended so far out and made it very unbalanced. When I get the new tool bit that should make it so I can get a higher RPM.

Originally Posted by LeeWay I find a random orbital sander the best for finishing out a rough surface in graduated grits.

You read my mind I was just looking at the ones from harbor freight yesterday.

Originally Posted by LeeWay Chrome is pretty unforgiving on anything but a perfect surface.

That I know. I never really noticed it until I was looking at how it was flaking off the mounting brackets on my motorcycle. On close inspection I could see the buffed out machine marks.

Thanks for the quick response Lee.

Rick

[ALLtra Mach]

Through them damn flycutters awa and buy a face mill.

[philwell]

Originally Posted by HackMax Hello folks. I can't seem to find exactly what I'm looking for as far as preparing aluminum for chrome plating by searching the net so I will put the question to you. I have a 5" x 9" x .625" piece of 6061 and on the one side I need to take all the extrusion marks out of it so it is flat for the chrome plating. I would like the surface as smooth as possible so I would have less work preparing it for the chrome. I have a Grizzly X3 conversion and I first tried a 3" carbide indexable mill and I soon found out how important tramming the mill is as it left a small ridge in the middle on the second pass. Even if the ridge wasn't there the surface it left was still inadequate for final preparation. I plan to sand down the final machine marks with 400, 600, 1000 grit sandpapers and then buff it so no marks show in the chrome. I thought I may be using the wrong tool so I tried a fly cutter with a carbide tool bit extended just a bit over 2.5" to cut it in one pass. The surface still was too rough for the first sanding. I've ordered an extra long square tool bit for the fly cutter so I can experiment with different cutter shapes and also help balance out the fly cutter for less vibration. I've tried different speeds and feeds but I'm not sure what would be optimum for either of these tools. It didn't seem to make a difference in the surface. Anyone out there have any ideas or thoughts on the best way to do this and get a half decent surface. What would the best tool bit shape be for the fly cutter. I've since trammed the mill and now the dial gauge doesn't move a lick in the rotation so I can try cutting in 2 or more passes again. I have already milled the piece I started way out of spec so it is pretty much trash for the project. I will use it as a practice piece. Thanks, Rick

You need rigidity in your setup number one the get a good finish. Use a tool with positive rake. And try using a little white kerosene as a lubricant. It may smoke a little but with improver your finish a lot

[HackMax]

Thanks fellas. I'm gonna try everything you throw at me to save me some sanding. I have tennis elbow in both arms and manual sanding is out of the question. I bought a random orbital sander a few days ago and will try that once I get the long tool bit for my fly cutter. I have what is considered a face mill I guess with a the 3" indexable mill I mentioned but it doesn't really give me a much better surface than the fly cutter even though it has 5 carbide cutters. Really I'm only grazing the surface at .005" and wouldn't expect the machine to be that loose that it would cause a rough surface but if all else fails I will tear the machine down and polish the gibs and lap the ways so I can make the table a little more rigid.
I haven't tried using kerosene but I'll give it a shot. I'm thinking with the fly cutter if I balance it out so it turns freely at most any speed it will cut the smoothest. I will give the positive rake a shot too. This will be my first bit grinding experience.

Rick

[LeeWay]

Some grades of aluminum just take machining better than others as well. WD40 also works pretty good as a lube on aluminum.

I try not to machine any 5000 series stuff. I typically order 6000 stuff and it machines nicely.

[TOTALLYRC]

Originally Posted by HackMax Thanks fellas. I'm gonna try everything you throw at me to save me some sanding. I have tennis elbow in both arms and manual sanding is out of the question. I bought a random orbital sander a few days ago and will try that once I get the long tool bit for my fly cutter. I have what is considered a face mill I guess with a the 3" indexable mill I mentioned but it doesn't really give me a much better surface than the fly cutter even though it has 5 carbide cutters. Really I'm only grazing the surface at .005" and wouldn't expect the machine to be that loose that it would cause a rough surface but if all else fails I will tear the machine down and polish the gibs and lap the ways so I can make the table a little more rigid. I haven't tried using kerosene but I'll give it a shot. I'm thinking with the fly cutter if I balance it out so it turns freely at most any speed it will cut the smoothest. I will give the positive rake a shot too. This will be my first bit grinding experience. Rick

The correct inserts for aluminum will make the a world of difference. The cutteres should be very sharp, as opposed to slightly rounded like cutters for steel, if I remember correctly, I did a test cut with the face mill I picked up and I got a very shiny, very smooth finish that wouldn't be to hard to polish.

I will post pics if you would like.
Mike

[HackMax]

Originally Posted by TOTALLYRC The correct inserts for aluminum will make the a world of difference. The cutteres should be very sharp, as opposed to slightly rounded like cutters for steel, if I remember correctly, I did a test cut with the face mill I picked up and I got a very shiny, very smooth finish that wouldn't be to hard to polish. I will post pics if you would like. Mike

Aha maybe that's why the face cutter didn't do as well as I expected. The inserts have a radius at the point which I thought would be better for getting a smoother surface. So I now have to get some pointed inserts too.
I am having a difficult time tramming the mill though so the face cutter will still leave a slight edge. It only needs one little piece of paper as a shim and the head goes too far. So I'm moving the paper up and down to vary the position. I suppose I'll have to get some shim stock as well.
I can't believe all the slop that is in the column if the gib isn't tight. I need to work on that also to give the normal machining a better finish. What the problem is there is that when I adjust the gib to the specs I can live with the Z has a hard time getting back up the column all the way. I have added a gas strut to the system recently and that has help considerably. I even tighten the gib lock up a tad while 2.5d milling.
If you have pics handy I would like to see what I should expect to get. Thanks.

Thanks Mike.

Rick

[HackMax]

Originally Posted by LeeWay Some grades of aluminum just take machining better than others as well. WD40 also works pretty good as a lube on aluminum. I try not to machine any 5000 series stuff. I typically order 6000 stuff and it machines nicely.

I use WD40 when I cut as it is now because I want to go flood cooling but I haven't built the enclosure for the mill yet. I think maybe I'll put together a tray around the table and see if that will contain the fluid for now.

Thanks Lee

Rick

[ALLtra Mach]

Totally RC is totally correct, the right inserts are a must. You DO NOT want coated inserts for aluminum. Look at what is available for your cutter, call the manufacturer and ask them what grade to use. An aluminum insert will be super sharp, be carful just handling them. Kerosene, wd 40, purpose made coolant, what ever you use, use plenty of it. Spin the tool fast, aluminum will not burn carbide.
With that shallow cut, you will not need a high feed rate to stop chatter, you want to cut very free and easy and it will polish like a mirror.

[HackMax]

Originally Posted by ALLtra Mach Totally RC is totally correct, the right inserts are a must. You DO NOT want coated inserts for aluminum. Look at what is available for your cutter, call the manufacturer and ask them what grade to use. An aluminum insert will be super sharp, be carful just handling them. Kerosene, wd 40, purpose made coolant, what ever you use, use plenty of it. Spin the tool fast, aluminum will not burn carbide. With that shallow cut, you will not need a high feed rate to stop chatter, you want to cut very free and easy and it will polish like a mirror.

I can probably just take the tool to the supply shop near here and get the right inserts. It is just a cheapy import. I have to go up there so I will take it with me once the snows let up.

I tried the sander yesterday and it worked pretty well. It took out all the extrusion marks but I need to get a finer grit. I used 120 grit and then had to block sand it with 400 grit to get all the swirlies that the sander made but it leveled the surface without facing it. I think once I get the proper inserts I should be able to use a finer grit on the sander and just block sand it with 800 and polish it from there. After the 400, then the 800, i got a smooth as glass polishing on the metal.

Sure would be nice to just face it and polish it - would save lots of time.

Rick