Quote Originally Posted by bradywatson View Post
If the only purpose of the Sintra is to protect the mirror, then I would just get a 12 or 24" roll of transfer tape, which is like masking tape, available through sign supply houses & cover it with that. It's cheaper in the long run. I don't know how you are attaching the Sintra to the mirror - ???

Sintra cuts beautifully on these machines with a single or double o-flute. So it isn't an issue with the right geometry. You can get by with an end mill, but the finish is not as nice.

FYI - ShopBot has techs in your area that can give you training and tune up the machine in your shop. Call them to inquire. 2 days of training would pay for itself in no time considering you'd be 'getting all the answers' to your questions right away.

Your 300Hz spindle is fine. It's nice to have a few extra RPM, but there is no impediment to you cutting what you want.

You don't want to use a BALL end mill - if for no other reason than you will be left with a cusp on the parts that looks like this---> л - which is probably NOT what you want. You could get around this by burying the bit into the table until it no longer imparts a cusp on the edge, but this is frowned upon for a number of reasons.

-B
We have applied 3m pre-mask to the front surface of the mirror prior to cutting. The sintra is applied to the back surface to protect the mylar mirror part during cutting but also when these individual pieces get glued to the final support - wood columns. So there has to be some kind of backing for gluing and sintra was recommended due to its ease of cutting and porousness - the recommended adhesive is silicone for flexibility. The mounting material is also silicone based for flexibility between the acrylic mirror and the sintra. It is a pressure sensitive film called opti-clear.

Also, I realize now that one of the tests that I posted pictures of (the 2ips letters, the most wobbly ones) were solid sintra, not this laminated acrylic sintra thing.
These tests were cut .05" into the sacrificial LDF board to avoid the ball part. The tabs that I used definitely show the curvature and it is not great for the part. But since I have now two ball nose tapered bits in shallow angles, can you elaborate more on what the drawbacks of cutting into the LDF are?

I am now planning on several approaches for testing.
1.2 pass profiling : rough cut with Oflute unbeveled, followed by tapered end mill.
2.Ball nose bits we have purchased, in two passes first to clear the sintra, adhesive and mylar then 2nd pass to cut the acrylic itself.

I will be tugging and pushing on the head tomorrow and tightening anything that I can find. That said, I am certainly going to push for us to have a shopbot person come by to check out our setup and give direct suggestions.
I'm assuming that I ought to contact Shopbot directly for this, correct? You don't know anyone in the general Southern California area do you?
Thanks