Cutting Aluminum with a Router

[Luke Maddux]

Up front, sorry for posting in General, but I wasn't sure where this belonged since it was about cutting metal with a woodworking tool.

I'm on a job and we take sediment cores from the bed of a river. When they come up, they are in a plastic tube inside an aluminum tube. We are trying to devise an effective way to cut the aluminum tube without cutting all the way through the plastic tube. We've tried a couple of things and they aren't working, so the new idea is to use a router.

My idea is fairly simple. Buy a powerful router, screw two parallel boards to the base of it to serve as a guide which will allow the router to slide down the length of the 6ft long, 4in diameter Aluminum tube without rocking. Then, put a 60deg, carbide tipped, v-shaped bit into it, and set the stop so that the tip of the V barely projects through the Aluminum without cutting clear through the plastic. When it's time to cut, plunge the router through the metal and use the two guides to make a cut down the length of the tube, then roll the tube around 180deg and make another cut, effectively splitting the tube.

In my mind, this seems like it would be effective and safe, but I don't know much about cutting Aluminum with carbide at 20,000rpm.

Can anyone provide any advice on how well this is going to work? I should probably mention that our budget on the router and a dust collector is practically unlimited, so I'm just going to buy a Festool. Also, there's a bit of moisture involved, but I don't expect that it will be flying everywhere, but a bit may get into the collector.

How does a dust collector do with aluminum shavings?

Really, I'm open to any thoughts or suggestions.

Thanks,
Luke

[Bohdan]

The problem with using a V router cutter in aluminiun is that the cutting tip is very small and as a result the ali will tend to stick to the cutter and clog it up. Once that happens the rest of the cut is just generating heat and this will make the glogging worst.

I think you would get a better result making a jig that will accept and hold the 4" pipe so that a track saw can be used.

An expensive track saw option is the one that is specifically designed to cut a V groove in aluminiun.

http://www.festool.com.au/epages/tooltechnic.sf/en_AU/?ObjectPath=/Shops/tooltechnic/Products/575003/SubProducts/575003

The dust collector will have no problems with the metal flakes but if you use a liquid lubricant it will in time oil up the inside of the hose and cause problems when used with wood. This would be solved by using a dry lub.

[BobL]

I've done a fair bit Al routing and cutting with WW gear, I got the idea from watching my BIL who is an Al boat builder and uses many WW power tools in his work.

Routing on edges is straightforward, rub hard wax onto the edge and use router as per usual.
The wax is essential or the Al will gall onto the edges and if left unchecked it will make a complete mess.
If a bit of galling appears the finish will not be as good but it will still keep working for a while.
I use a slow speed than 20,000 rpm, typically 15,000 rpm

Routing slots is somewhat trickier.
If the bit galls, even just a wee bit it, rattles the bit in the slot can then grab and shake the shyte out of the workpiece making the slot wider and rougher, and even breaking bits.
You'll need more force than cutting wood so you can't use really small bits unless they are brand new and then they only last for a few cuts before they need cleaning.
On a sediment core tube I could even envisage it grabbing the tube and cutting crooked.
If you did not want to risk the bit grabbing and cutting through the plastic you'd need think about the pros and cons of the bit type.
Up cut will dig in possibly penetrating the plastic, and down cut will spray the plastic with swarf, could even melt the plastic.

The way I would do this is with a Table saw with a negative raked toothed blade and set the TS up with a suitable stop high high enough above the blade so you could rotate the core tubes.
The blade I bought a few years ago was a Chinese Bosch blade ($69) and that is the blade I tend to leave on my TS, as well as Al it cuts brass and plastics and also wood - but very slowly.
The negative raked teeth are essential because they don't pull the work into the teeth but push the work away and scrape away the Al.
I would make and install a guard to completely cover the blade except for the depth of teeth needed to cut the Al tube.
Hard wax rubbed on the workpiece and blade teeth would reduce the likelihood of galling.

Whatever you use the savings are like little razor blades so full face protection is needed - my DC sweeps those from a TS away but using a router table is considerably less effective.
Also your tubes will get in the way of dust/swarf collection but you will have to live with that.

Meths is a fantastic lube for Al as it leaves no mess BUT you need to be careful and not have ANY sparks happening. to work properly you need to apply lots of it and thus you cannot use it for very long because it will fill the shed with vapour - i.e. flammable and can make you very sick. I use meths on Al, mainly on a DP, BS and metal lathe, especially with Forstner bits, and apply it with a hand pump spray pack. Wax works better on a TS and router.

[elanjacobs]

I agree with Bohdan, a circular saw is probably a better option than a router

[rrich]

From a safety standpoint, I would use a table saw. Build a sled that can be clamped to the table. Make it a "V" to hold your plastic / aluminum. Raise the blade through the sled just enough to cut into the plastic sleeve. With the saw running, gently put the plastic / aluminum into the "V". Hold the left end with your left hand and press down with your right. Use your left hand to turn the plastic / aluminum in a clockwise direction.

[rrich]

Another thought that is even safer. Just use a pipe cutter, one of those hand operated ones with a couple of rollers to hold the pipe and a cutting wheel.

[BobL]

Another thought that is even safer. Just use a pipe cutter, one of those hand operated ones with a couple of rollers to hold the pipe and a cutting wheel.

Unfortunately this won't help with the longitudinal cuts down either side of the tube.

[RobbieB]

How thick and long is the tube? A caustic bath will dissolve it pretty fast, but won't affect the plastic. Can you plug the ends and leave it in caustic overnight?

[BobL]

How thick and long is the tube? A caustic bath will dissolve it pretty fast, but won't affect the plastic. Can you plug the ends and leave it in caustic overnight?

The caustic will get into the sediment cores so I doubt that is a practical solution. :)

[Luke Maddux]

Yeah, definitely no wax, caustic, etc. We're taking lots of samples which need to measure contaminants in parts per million, billion, and even trillion, so nothing can be added.

And I also found out today that I misunderstood my boss... The tubes are not Aluminum, they're Lexan plastic. This will cut like butter and likely without any problems. I almost feel bad buying Festool gear to do the job...

Almost :D

Anyway, thanks a lot for the insight. If I ever do need to cut metal I've got a much better understanding.

Cheers,
Luke

[BobL]

Yeah, definitely no wax, caustic, etc. We're taking lots of samples which need to measure contaminants in parts per million, billion, and even trillion, so nothing can be added.

And I also found out today that I misunderstood my boss... The tubes are not Aluminum, they're Lexan plastic. This will cut like butter and likely without any problems. I almost feel bad buying Festool gear to do the job...

Are there now two plastic tubes?

[Luke Maddux]

Are there now two plastic tubes?

There are dozens, maybe hundreds. I'm honestly not even sure. Each core comes in a tube, and we're collecting many hundreds of cores, but only a portion (of size unknown to me) come in the tubes which must be cut with power tools.

[BobL]

There are dozens, maybe hundreds. I'm honestly not even sure. Each core comes in a tube, and we're collecting many hundreds of cores, but only a portion (of size unknown to me) come in the tubes which must be cut with power tools.

I meant are the Lexan plastic tubes over the top of an inner plastic tube?

[Luke Maddux]

I meant are the Lexan plastic tubes over the top of an inner plastic tube?

Oh, sorry. No, it's just one tube around a core.

[rrich]

Another thought.

Use a table saw. Set the fence to half the diameter of the core Lexan thing and subtract half the saw kerf. Set the saw blade height to almost the thickness of the Lexan. Run the core in the Lexan through the saw. Roll the core 180° and cut again. Use a large flat blade screwdriver in a twisting movement to separate the Lexan tube.

[BobL]

How solid are the sediment cores themselves - I'd be worried they would disintegrate and made a mess - not to mention they would lose their all important self integrity?
How much moisture do they contain. If they are still moist and freezing would not alter what was being measured, then freezing them first might be enough to hold them together while the plastic tube is being cut?

[ian]

Hi Luke

That's a curly problem you have there.

The way I see it, the tool you use is less important than being sure that you avoid cross contamination between cores.

We're taking lots of samples which need to measure contaminants in parts per million, billion, and even trillion, so nothing can be added.
I don't think a circular saw will cut it (please excuse the pun), even if you use a new blade for every core. Too much risk of contaminating the sample.

are the cores sufficiently uniform in diameter and lexan thickness that a saw could cut almost but not quite through the lexan?

do you sample a whole 6' section of core or only small sections of it?
if it's small sections, can you use a pipe cutter to extract the (say) 6" long core sample, drop the section into liquid nitrogen to snap freeze it than push the snap frozen sample out of the tube?


also, what you are doing is not "unusual". I'm sure the geologists and core drillers I worked with in the past had methods of extracting sand and silt samples from a core -- I recall two part sleeves that just separated when you placed the core on the storage tray.

[BobL]

I have some experience setting up ultra clean labs used for cutting up and decontaminating polar ice and sediment cores so presumably some decontamination process will be needed.
This is because the core drill (and in case of the ice cores, kero lube used) cross contaminates the layers on the outside of the core.
Plastic sediment cores are usually just pushed into the sediment but some degree of layer cross contamination occurs on the outsides.
Decontamination usually involves stripping away the outer layers of each core.
In the care of 100 mm diameter cores we used to remove up to 37.5 mm from the outside leaving a 25 mm inner core which we did measurements on.
Isotope measurements of the shaved ice were used to track contaminants right into the inner core dues to cracks in the ice - these sections of core had to be discarded for the most sensitive measurements

At once stage we used SS blades driven by a power drill and a flexy shaft to removed the outer core layers by cutting slices along the core lengths.
We had 11 separate SS blades and used to cycle them through nitric acid cleaning baths cleaning baths.

A special ice core holding "indexing lathe" made of acrylic, teflon, and SS was made to hold a short sections of core while the blade travelled along the length of the core.
The lathe/rig had to operate at -18ºC in an ultra clean lab and so was driven pnuematically for cylinders of ultra clean nitrogen.

The rig was only used with circular blades for a short time before the decontamination methods reverted to using custom made SS chisels (see second photo) to shave small amounts of ice of the core at a time as this was deemed safer and produced less cross contamination. The contamination of the ice by the chisels was tiny but significant and had to be subtracted along with other contamination from the measured results.

422820
422821

15 years on and a completely different method is now used.
The outer layers of the core are cut away with a BS and the inner half melted vertically on a slotted SiB (bluish) hotplate with holes in the bottom.
This rejects all bar the inner 20 mm section of the core and the liquid water goes direct into analytical instruments for analysis
422822

The lathe went into retirement, then surplus and finally it disposed of last year and I managed to get hold of most of the bits and pieces and still have them. I made my TS OH guard from one of the chunky pieces of acrylic.

[Luke Maddux]

We do have to focus on cross contamination, but not to the point of glove boxes, fume hoods etc. We just use a lot of clean gloves, plastic matting, tyvek suits, etc. We also decontaminate everything thoroughly.

When the core is cut (some of them can be opened with mechanical shears) it will ooze out a bit, but not much. It's high in silt and clay content, so it's relatively well consolidated.

I've bought 5 bits which can be used for cutting acrylic. Solid carbide so they shouldn't rust. I've gotten a Festool router with an adjustable fence and a dust collector. My plan is to set the plunge depth such that the bit will project just through the acrylic and not sling mud everywhere. The oozing effect of the sediment has a bit of a delay, so I think that moving the router with a solid feed rate should be more than enough to avoid soaking it in mud. Using the fence should eliminate the problem of the router wobbling, and keep the bit centered. It will still be able to drift, and won't cut a perfectly straight line, but we don't need that.

I think it's going to work... I have faith that I haven't blown it too badly here and it'll all be fine.

I will know Monday... The router came without a fence, so Festool is overnighting one to me and it arrives then.

Cheers,
Luke

[Luke Maddux]

Sidenote: Bob, what do you do? In another lifetime I was a glaciologist. I wasn't involved in ice core analysis, and was more on the fluid dynamics side.

[BobL]

Sidenote: Bob, what do you do? In another lifetime I was a glaciologist. I wasn't involved in ice core analysis, and was more on the fluid dynamics side.

I've been retired for 4+ years but in another lifetime I was an academic in a University physics department. The research I was involved in required the use of ultra clean air laboratories (hence my interest in dust) and built a complete 6 x 4 m clean lab back in 1985/6. I did all the plumbing (all plastic), electrics, built the PP and HDPE ducted air filtration/handling/extraction etc from 8 x 4 sheets of plastic and the lab benches were made of plywood and finished with 7 coats of epoxy. It was cheaper to employ me as a uni researcher than to get all the different tradies involved. It was only just possible within a Uni environment to do that back at that time whereas these days it would just not be permitted. I have also been involved with the design and building of 3 other clean labs.

[Bohdan]

My plan is to set the plunge depth such that the bit will project just through the acrylic and not sling mud everywhere.
Luke

I would set it just short of full depth so that the very thin remaining piece could be cut with a box cutter and avoid all of the mud slinging. :U

[ian]

I would set it just short of full depth so that the very thin remaining piece could be cut with a box cutter and avoid all of the mud slinging. :UAgree


I'd also mount the router on a morticing jig -- the type that straddles the piece being morticed.
That way the cutter should stay centered on the core.

[ian]

I've bought 5 bits which can be used for cutting acrylic. Solid carbide so they shouldn't rust. I've gotten a Festool router with an adjustable fence and a dust collector. My plan is to set the plunge depth such that the bit will project just through the acrylic and not sling mud everywhere. The oozing effect of the sediment has a bit of a delay, so I think that moving the router with a solid feed rate should be more than enough to avoid soaking it in mud. Using the fence should eliminate the problem of the router wobbling, and keep the bit centered. It will still be able to drift, and won't cut a perfectly straight line, but we don't need that.

I think it's going to work...

I will know Monday... So, did it work:2tsup: , or are you covered in mud? :hmmm:

[Luke Maddux]

It worked! It was highly praised by the project manager.

It's a pretty horrific cut, but it gets it done. It is jerky and by no means straight. Lexan is one hell of a material. Nonetheless, none of that matters as long as we can scoop the core.

No mud slinging either. The projection is perfect.

Now to just convince them to give it to me when the job is done... :)

[BobL]

It worked! It was highly praised by the project manager.

It's a pretty horrific cut, but it gets it done. It is jerky and by no means straight. Lexan is one hell of a material.

Glad it works.

If you want a dead straight line use a negative raked circular saw blade, it cuts Lexan like butter..

[ian]

It worked! It was highly praised by the project manager. doesn't get much better than that


Now to just convince them to give it to me when the job is done... :)crossing my fingers for you

[ian]

for future readers, a link to this information on milling plastics was posted on the Metalwork forum
Selecting the Right Plastic Cutting End Mill - In The Loupe - Machinist Blog (http://www.harveyperformance.com/in-the-loupe/choosing-right-plastic-cutting-end-mill/?utm_source=Pardot_Email&utm_medium=Email&utm_campaign=Harvey_Email_PlasticCutters)