New SB Desktop – not a machine person. Help?

[quniform]

Hey Shopbotters,
I just received my new Shopbot Desktop! Woa! I am setting up now.

All I am using this machine for is one type of project: I will be carving detailed, photo-based, low reliefs into acrylic sheets (It's an odd project – the carvings will function as molds that I will make casts from.)
Relief Depth: 1/4 in.
Size: just under 18x24 in.
Bit Size: 1/8 in.

I am a computer graphics person. So the software part is easy for me. It's the mechanical, physical, and material issues that are intimidating.
Please bear with me on such basic questions, as I have zero experience with tools, bits, routers, cnc, etc.

Questions:

1. What's the best way to set up and attach a spoilboard to the t-slot base that the desktop comes with? Do I just bolt a piece of 1/2" MDF to the t-slot? Anything I should watch out for?

2. I don't have a vacuum system, how should I hold down the material? Do I need downward pressure, or do I just have to worry about side to side movement? Can I just screw a few scraps of MDF around the edges of the acrylic sheet to keep it in place? Should I clamp instead?

3. The machine time is going to be crazy – the test I had fabricated took 15 hours to get the detail I needed. I need the detail, but is there another material that I could cut faster?

Thanks so much.
I've already received many great insights from the forum.

Best,
Daniel

[oddcoach]

Hi Daniel
yes you can just screw a piece of MDF in place. Make sure you countersink the screws as deep as possible so you don't have to worry about hitting them while you are cutting.
learned that one the hard way. I am guessing the acrylic is thin . you might be better off using double stick tape to hold your parts. don't use carpet tape it is to thick and squishy.
I use a film tape from Shuretape DP 050
http://www.shurtape.com/Default.aspx?Tabid=79&Level1=34&Level2=70&ProductID=150
screwing mdf around the part will work but for a thin sheet you will some doublestick tape to keep the part from lifting in the center.
Very fine detail does take a long time to cut. I have made some small very detailed pieces for making molds from. I have found that machinable wax is a better material than acrylic. You can go a little faster but not much. your speed will be limited by the slowest axis which is usually the Z
I have gotten the best results from setting the xy speed close to the z speed and changing the ramping settings to .9
I don't know how small you will need to go. I have used bits down to 0.015 ball nose to get in the tiny places. I get them from www.razorsharpgrinding.com
they have tooling down to 0.005
hope this helps
John

[quniform]

Thanks so much John.
I appreciate the help.
Best,
Daniel

[bob_s]

There has been some mention of alternate materials for molds
take a look at http://www.talkshopbot.com/forum/showthread.php?t=11901&highlight=mold+making

I cut wood, but remember talking to Bill Palumbo at a shopbot event, and e as vast experience in making molds, may be worth PM-ing him for some suggestions

[oddcoach]

Glad to be of service. don't hesitate to get a hold of me if you need more help
John