Cutting Strategy

[jim_vv]

Greetings from Southern California,

I have a friend who asked me to cut some letters out of 1/2" sign foam for him. The capital letters are 13", the lower case are 10", and the numbers are 8". I have nested the letters somewhat "loosely" on the 4' x 8' material so that I can maintain as much vacuum as possible. I use two Fein vacuums with four zones for hold down. I plan to bridge the dots of the "i's" and plan to use a 1/4" Onsrud down cut end mill. I was thinking that I could pause cutting half way through and cover the cut half with plastic to maintain vacuum if needed. Does this strategy sound like it may work? Any suggestions? Thank you in advance.


5545

[coach]

Jim, I also use 2 feins. I think you will find the bit will pack the waste around the letters and they will be difficult to remove even after the vacuum is off.
I use tabs in 2 places on acrylic letters because the bit removes all the waste.
Keep us posted.

[joe]

Jim,

That's one way to go.

If this was my job, I'd put two 1/8"X.25" bridges on each letter and re-nest them. By doing so it looks as you can save half a sheet. Sanding little 1/8" bridges off HDU is a snap.

Another option which is cheaper, and I think even better, is to use PVC such as Centra, or Komatex. One reason is there isn't any priming and difficult finishing. Also, when routing PVC, if a strait double fluted bit is use, there isn't any reason for bridges or vacuum. The letters will stay in place.

You can throw a 1/2" PVC letter across the room and it won't break. Run over it with a car or do lots of other mean things to it and they are good to go. Which is to say, HDU is too expensive, too deliclate, and takes too much time to finish.

But what do I know?

[joewino]

I agree with Joe...what does he know?

Seriously, unless you client just requested HDU and will accept nothing else, I would use some type of PVC...for the same reason that Joe mentioned.

I use a lot of HDU but sometimes it is just not that practical.

[jim_vv]

Gentlemen,

Thank you so much for your valuable input. I very much appreciate you sharing your knowledge. My friend chose, is supplying, and will finish the material. All I am doing is the cutting. I will put two bridges on each piece, nest them closer and then use an up cut cutter. This forum is great! I will post my results next week. Again, thanks to all.

JIM

[curtiss]

Never thought of it, but it is nice to work with material that you can throw across the room when you are done. I am going to start throwning more stuff.

The letters look good, but some of the new layouts are difficult to spell check.

[GlenP]

Hey Guys, I had a bad day on Wednesday and threw quite a few things across the shop. Seems like everything I cut was the wrong size..broke two bits and by the end of the day I had wasted two sheets of material, broke two bits and nothing to show for my day. Oh well Thursday was better but tossing a few parts around the shop did make me feel better at the time. My wife usually looks through the window to check for the all clear before entering the shop on days like those.
When I cut letters I do not use vacuum. I use a 1/4" double flute end mill and the kerf usually fills with shavings and holds the part in place while cutting. I have at times not cut all the way through the material and left a very slight onion skin (1/32") to keep the part in place and then just use a knife to finish up and remove the letter. It works great and keeps the smaller dots from being sucked up into the dust collector as well. Never tried on HDU yet but on extira and Komacel works fine.

[joe]

Glen,

This sounds like my shop. When I was throwing around HDU letters it was much more expensive.

I thought I was the only fellow on the planet who cuts PVC with a strait bit and no vac.

Thanks for posting

[john_l]

When you guys say straight bit... you mean just regular old straight as in the picture below, correct?


5546

[pro70z28]

Yup, mine have a longer flute but, yup.

[beacon14]

I would also leave an "onion skin" on the first pass, then cut all the way through on the second pass. If the kerfs are still full of chips at that point you might not need any tabs.

[jim_vv]

Thanks again to everyone for your input. I cut the letters today and everything went well. I thought I would post about my results in case it may be of help to someone in the future.

I used .25" x .125" bridges and nested the letters way closer. This resulted in covering less than half of the sheet. (I also ended up making the capital letters only 9" high per the customer's request.)


5547

In case anyone was wondering...the letters spell out
Hill Street Community Wellness Center
and 3130 as the address.

I used a .25" upcut spiral at 16,000 rpm at 1.5 ips in two passes (one pass would have been fine).

I am not a sign maker, but I am pretty sure that the material that my customer brought me was not HDU. He just said, "it is sign foam". It is more like a hard faced foam core. Does anyone know what it is called?


5548

Thanks again for you help!

JIM

[rb99]

Sintra?

RB

[don]

I'm going to guess that is Gatorfoam,
Gatorfoam is a foam that is sandwiched between a fibrous face and back. very light weight

[Gary Campbell]

The sign shops we cut for call this material PVC Foam.
Gary

[pro70z28]

Expanded PVC is what we call it. I did a grocery store logo with that stuff, has to be over 10 years ago. I think I used 3/4'' or there abouts. Painted it with red & green latex. It's still there.

[jim_vv]

I was able to look at the receipt for the material. Don, you were right, it was Gator Foam.

Thanks again,

JIM

[don]

I've used Gatorfoam a few times. ( I don't get much sign work)
But use a compression on that stuff, and do a test piece.
It cuts better going a certain direction, I forget which, either clock or counterclockwise.