So I bought a resurfacing bit for an uneven slab for a river table. What do I enter for the bit and how do I set zero?
Which tool did you buy?
For a possible starting point see the feeds and speeds for the McFly:
and for more see:
So to level an uneven slab first put it on the spoilboard and shim any areas that are a little off the surface. run the surfacing as a pocket a little bit bigger then the actual slab. I use a 1" Whiteside 6210 and use a depth of cut that is 0.010". Put pencil marks all over the surface and run the job as a pocket 0.010" deep with the same depth of cut. If pencil marks are left then zero on what you think is the lowest spot and run the job again.
After you get one side flat flip it over and repeat what you did on the first side.
Depending on how irregular the surface is you could increase the depth of cut but big bits in trim routers put a tremendous load on the Shapeoko and router. So be patient. The other advise is to run at a higher rate of movement i.e. IPM. Big bits tend to burn the surface especially on the corners where the bit pauses to make the turn. If getting burning decrease the depth of cut and increase the IPM.
You can use smaller bits but that takes forever on a big slab and unless your router is perfectly trammed you get a lot of little ridges. The ridges are ok because you will be surfacing the epoxy river off and have more chances to level the top up.
I use melamine molds sealed with silicone between the edges and the base melamine. Then I put Tyvek tape in the corners and base making an L shape. The Tyvek tape will not stick to the epoxy and makes mold release easier. You can also use some mold release to get the piece free from the mold. Deep pour epoxy is like water. If you have any leaks it will come oozing out. So make sure your mold is leak proof. You could also put the Tyvek tape around the outside of the mold for belts and suspenders.
Deep pour epoxy (all epoxy) shrinks when cured. You have to over fill to get a surface without a recessed area around the river. Also put some blocks on top and clamp the wood down because wood floats and it will rise out of the mold. Your surface placing the mold on needs to be perfectly level.
The deep pour epoxy is slow to cure and takes 12-24 hours to go from water like consistently to jello type consistency. So if adding color you have to stir the epoxy or all your color will fall to the bottom. Some people will fill the river partially and let it cure and then before full cure make a second pour.
Epoxy gets hot when mixed and get hotter when a large pour is mixed in a bucket. Mix your epoxy and when you think it is mixed mix it some more. I use a paint stirer to mix large amounts in a 5 gallon bucket. I dont mix 5 gallons but it is easier to mix large batches in an oversized container.
With wood and deep pour epoxy air will come out of the wood and cause bubbles. You have to run a heat gun or torch over the surface for a couple of hours to keep the air bubbles from erupting to the surface and making a splash or volcano appearance on the surface. Those type of bubbles happen just before the epoxy is cured enough and just when you thought you were through with the torch it happens.
If you have not poured deep pour epoxy have everything ready and waiting. You dont want to be searching for something. Keep some paper towels around and some acetone to clean up oops. Acetone will remove uncured epoxy off the floor and table tops. Acetone can remove cured epoxy if you soak it long enough. Epoxy is a messy process and be sure to wear gloves to keep it off your hands.
If adding colorant mix it in a smaller container and then add it to the main batch. This helps with the mixing. You have to scrape down the sides and bottom of your container often during mixing or you can get undissolved powders (like mica). I have used transtint aclohol based dyes and Alumnalite resin dyes with good success. I have also used powders that can give the appearance of moving water but you must stir the epoxy after a few hours before it becomes jello like consistency or it is all at the bottom.
When surfacing the epoxy it will be dull as dish water. Simply sand to 220-320 and get it as scratch free as possible. A good top coat will make it shine. Oil based Polyurethane will go right over epoxy. Water based might work but water and plastic (epoxy) do not mix well. By giving the surface some tooth at 220-320 the top coat will stick.
Sorry to be so long in my uninvited explanation but I have done a few epoxy jobs and learned a few things.
One more thought is if your colorant will make the river opaque is to put a piece of wood in the bottom of the river and not have to use as much epoxy. If it will not be seen you can save a little money and still get a good looking river table. If you use a filler you can hot glue it down because wood floats.
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Thank you for the detailed explanation I think I can figure it out now.
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