Cutting .050 letter backs

[vitals]

I am a new user and and having a hard time with cutting .050 prepainted aluminum for channel letter backs. I am using a Onsrud 63-606 up bit and have tried many many settings.I have a standard shopbot with a Porter router.I can get an OK cut, with a slight buhr on the top edge and my cuts have slight choppyness on the edges. I am screwing the 4' x8' sheet down to the table with cardboard between the sheet & the mdf top. Can anyone give me advice on feeds & speedsfor this typeof setup?

[road_king]

Hey John,

Check out the "Message Board".

Brady made a suggestion for you!

GB

[wcsg]

I can help you with this John.

What speeds can you go John?

[Brady Watson]

Double post...

Conversation going on over here (http://www.talkshopbot.com/forum/messages/312/36846.html?1229718990)

-B

[vitals]

Eric -10,000, 13,000, 16,000, 19,000 and 21,000 rpm are my router speeds

[wcsg]

Okay. I read some post from the other thread and it sounds like your set up is alot like mine.

Since we both don;t have a vac which would make the job a little easier as far as hold down goes it's best for you to stick with using your max of 21k RPM and move .5 IPS on a single up spiral bit 1/8"CED. I use Belin bits, I have both up and down bits. Our backs range from .040 - .080 depending on the size of the letters. Since I have a lack of hold down as well moving .50IPS makes it easier for me to use a little bit of carpet take and a few planned out screws. I just have to watch how much pressure I put on the screws as it was pointed out too much pressure bows the metal and can make it pop up.

As letter backs go the edge is good with explained above and you won't get burs or burns, you can make it better but the hold down is key. But again these are just letter backs that get returns put on. I would go with a down spiral bit if I were you, that way you don't have to worry about some flying debris caused from the centers of "R"s and such.

You can use bigger CED bits to move faster but you will need more hold down. I usually create my files with an initial drill file than places panned out holes for drywall screws then fasten that, then follow up with my profile cutting.

For cooling since the 1/8" will draw more heat I use a Vortex cool tool hooked up to my compressor that blows -100 deg air right on my bit making it last longer. Also known to leave a better edge on acrlyic

Vortex:
http://www.thesignsyndicate.com/forums/index.php?showtopic=1394


Hope this helps some

[Brady Watson]

Erik,
You usually don't need cooling if you run at the proper chipload and have vacuum hold down. You can build a vacuum holddown system for less than the cost of a Vortex cooler. Cranking the RPM all the way up drastically lightens the chipload, but generates gobs of heat, which reduces cutter life, and causes the chips to weld back on the part...unless you run a Vortex etc...Just an observation.

-B

[wcsg]

How much are we talking we can build a vac hold down system for? A Vortex is only $200 or so plus a compressor if you don't already have one. I'm getting a pretty good chip load from my feed speeds for a 1/8" CED.

What speeds have you run yours on for alum this thin Brady? And you are right, I probably don't even need the vortex on for this thin a metal, but I'm a creature of habit

[Brady Watson]

You can build your own setup for around $150. I started the Open Source Vacuum (http://www.talkshopbot.com/forum/messages/28/22456.html) thread a while ago, and many have jumped in and improved on my original concept (which was the whole idea...) - so not sure what motors are available now, but it's worth a looksy to get people out of the stone age with holding things down on their machines. (I have to admit, when I 1st heard about vacuum hold down I thought the notion was ridiculous & thought it was a waste of time)

I usually run a short (.25" LOC) 1/4" single spiral-O and cut between 13,000 and 15,000 RPM at 0.7 t0 1.5 IPS depending on the thickness of the material, and what that particular alloy likes.

-B