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Milling Odd size channel in one pass ?

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ZombiWelder

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#1
Howdy everyone!
A friend asked to make an aluminum and lexann decorative thingy, it called for 1/4 lexan to be sort of Dado'ed into aluminum. First thing I learned that in US there is pretty much no such thing as .250 polycarbonate. It's either. 220 or .236 . I order some pieces and the .220 turned out to be .226 and .236 turned out to be .230 Metric polycarbonate is not readily available. This is not a real job or anything and making this work is not terribly complicated but I wondered if you can stick and end mill into a boring head and off set it a few thausands to mill a slot or whatever , say take .219 end mill and make it cut .226 or are there some clever ways to avoid multiple passes I'm situations like this ? Aluminum, light passes, sharp toold etc.. I'm still on the market for that awesome deal on a used quality boring head, but I might just pull the trigger on an import they are not all that terrible apparently.
 

derf

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#2
1. Make it .250", fill the slot with clear silicone.
2. Use a 3/16" end mill, multiple passes.
3. Use a re-grown end mill.
Any reason you can't make multiple passes?
 

higgite

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#3
The difficulty I see with that approach is that the end mill will not be spinning. It will be moving in a circle as the boring head spins, but the end mill itself will not be spinning. That means you will only be cutting with one flute and that flute must be perfectly oriented in the boring head. Similar to a boring bar. What’s wrong with making multiple passes with a standard end mill?

Tom
 

ZombiWelder

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#4
The difficulty I see with that approach is that the end mill will not be spinning. It will be moving in a circle as the boring head spins, but the end mill itself will not be spinning. That means you will only be cutting with one flute and that flute must be perfectly oriented in the boring head. Similar to a boring bar. What’s wrong with making multiple passes with a standard end mill?

Tom
Lazyness primerilly, and that I haven't quite figured this mill out yet, it's a Chinese mill I got on a cheap, she's got it where it counts more or less, spindle runout, flatness, power etc. But the dials are not very useful .001" increments mean different thing on all 3 axis, and the back lash seems different every other day, which might be something I should figure out first I guess. I bought a cheap DRO kit that has about .005 repietability . My indicators are repietable and accurate, and with some patience I can mill parts to about .001 accuracy but it tends to take more time than it should somehow
 

brino

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#5
Hi ZombiWelder
it sounds to me that this project is a good one to learn more about your mill.
having to make extra passes will give you even more time to get comfortable with speeds and feeds, etc.

to deal with backlash be aware of climb vs. conventional milling when widening the slot.
climb milling will try to grab the work and pull it in to the cutter, possibly breaking it.
-brino
 

Eddyde

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#6
I have worked a bit with polycarbonate, the thickness can vary a few thou even on the same sheet. As far as I know, it's all made to metric sizes .236 is 6mm.
 

ZombiWelder

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#7
I have worked a bit with polycarbonate, the thickness can vary a few thou even on the same sheet. As far as I know, it's all made to metric sizes .236 is 6mm.
For whatever reason my local home Depot and professional plastic supply stock .220 even first two pieces of .236 I ordered from amazon were .220
 

Mitch Alsup

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#8
You are going to want to take at least three passes anyway.
1) Gouge out the center
2) put a nice finish on one side
3) put a nice finish on the other side.

Part 1 takes most of the time anyway, the other two passes are light cuts.
 

ZombiWelder

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#9
You are going to want to take at least three passes anyway.
1) Gouge out the center
2) put a nice finish on one side
3) put a nice finish on the other side.

Part 1 takes most of the time anyway, the other two passes are light cuts.
The KISS principle hardly ever failed me (keep it simple stupid ) but I do like to understand what the heck I'm doing and there's that thrill of figuring out some weird way of doing something
 
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