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Profile cutting 1" aluminum with a 1/4" endmill.

Pattnmaker

Stainless
Joined
Nov 2, 2007
Location
Hamilton, Ontario
I recently quoted a profile cutting job cutting a 1/2" 4x8 sheet of aluminum into around 120 letters and numbers. I had planned on doing this on my CNC router that has a Fogbuster MQL system set up on it using a 1/4" streaker endmill. The router is all ballscrews and I have used it to cut aluminum coreboxes in the past. I had planned on cutting it in 4 steps of depth and with a roughing and finishing pass mostly to help clear chips and prevent binding. Lots of passes but a pretty high feed has worked well for me in the past with the router which while fairly rigid by router standards is pretty flimsy by metal cutting standards.

My customer has now told me that he made a mistake and about 80% of the letters (all the ones with the tightest corners) are actually 1" aluminum. Suddenly I am far less confident I cannot choke the endmill up like I had planned and the MQL Lube is less likely to reliably make it to the bottom of a deep slot.

I am now wondering if a corncob cutter to rough makes more sense then a finishing pass with the streaker? Or just space the letters out more and widen the slot?

Another option would be to have the sheet cut up into 30x24" pieces and cut the job on my new to me Machining Center. It would end being the first job on the machine. Disadvantages would be more difficult hold downs, machine is not 100% ready to go yet 99% but not quite there, and extra material waste. Advantages would be the extra rigidity, Flood coolant, and smaller pieces I would be less worried about the middle of the sheet lifting so I could leave a thin skin on the back to break out rather than adding and cutting tabs which will be a lot of extra work.

I would love to hear some thoughts on this.
 
Can you use a reduced shank endmill with short flute length to get better overall stiffness? Something like this: Reduced Shank 1/4 3 Flute End Mill Finisher 4.0 long X .236 Shank MariTool

I would probably try smaller axial steps, maybe 0.050" or so just to minimize the volume of chips you need to clear, crank the air pressure on the MQL system and have a shot! With one-off things like this I tend to run really conservative, especially when material cost will be relatively high like in this case!
 
Oh and if you can: program it as a continuous downward ramp/spiral around the letter to your final height. Not having to plunge or have short ramps really smooths things out and will eliminate dwell marks and other weirdness...
 
I'm curious as to what you've worked out with the customer as to minimum radius on inside corners. Just about any font out there is going to have very large quantities of sharp inside corners that are not possible without wire edm.

I'm leaning towards getting your feet wet on the new mill. Draw out your machine table in CAD including t-slots and max travel and see how the letters and numbers fit. Devise layouts that can use the t-slots for predrilled hold downs. Perhaps do the entire job on top of some cheap HDPE. You could also use the edges of the stock for at least one leg that you'll find on numerous letters, leading to much less slotting you have to deal with.

On 1" stock I'd lean more towards a 3/8 cutter or more for roughing in two to three passes tops if you have enough work holding security. I would not fight this thing just to save money on stock. It won't be worth it. With all the slotting you're going to end up needing a finishing pass on everything so plan for that. Might be your best moment in time for the final cut through if only a few thou remain.

Just thinking out loud.
 
Another option would be to have the sheet cut up into 30x24" pieces and cut the job on my new to me Machining Center. It would end being the first job on the machine. Disadvantages would be more difficult hold downs, machine is not 100% ready to go yet 99% but not quite there, and extra material waste. Advantages would be the extra rigidity, Flood coolant, and smaller pieces I would be less worried about the middle of the sheet lifting so I could leave a thin skin on the back to break out rather than adding and cutting tabs which will be a lot of extra work.

I would love to hear some thoughts on this.
Your mill HAS to be better for this job than a router. This is the route I would go. And have a look at the Destiny Diamondback end mills, they love aluminum.
 
Clearing chips with the router is going to be a huge issue. At some point there will be a mountain on the sheet that will be a problem. Air/lube blast + vacuum extraction. Good job for a cyclone separator.
I think with either machine you will be baby sitting the process. Maybe break the program down to 20 letters at a time and those letters are scattered all over the sheet. That would prevent the chip mountain from forming. Vacuum off between programs.
 
Just spoke to the customer and the Price has killed the 1" thick letters. He is just going to cut them out of plastic and paint them. He will do that himself. He has a light duty CNC router.

I still have to cut the half inch aluminum letters but those letters have really big rads in all the corners and I am not worried about them. There are only about 20 of them and I can use a short 3/8" end mill.

Thanks for all the advise. I can't say I am that disappointed in losing the 1" thick letters.
 
Sub it out to someone or a big laser it could do it so cheap you both could make money on the job


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Yep. I used to do a ton of this stuff. We had a large router, waterjet, and laserjet. Both the 1/2" and 1" job would have gone straight to the waterjet.

EDIT: P.s. Is 1/4" the largest tool your router can hold? I've used 3/8 onsrud single flutes and downdrafts with good results many times
 
We did consider subbing out to waterjet but it would definitely have a different finish and they would definitely notice the difference. This customer is a neighbour signmaker and we do some cutting for them when their router cannot do the job or involves 3d cutting or gluing up wood.

We can use and often use up to 3/4" endmills for wood and plastic. I keep to 1/2" and smaller for aluminum on the router.
 








 
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