ShopBot Table expansion

[dlcw]

I used 3/4" Baltic Birch (or Appleply - American equivalent) layered 2 pieces thick, for my table surface (5x8 machine) and 3/4" LDF for my spoil board. The Baltic Birch is very stable. We have below 0 winters and 90-100+ degree summers with varying humidity levels year around (almost no humidity in the winter and high humidity in spring and fall, with humidity all over the place in the summer). Nothing like the south though. LOL!

I always use a 1/8" piece of MDF as a sacrificial sheet on top of my spoilboard so I don't cut into my spoilboard. I cut a LOT (800-1000 sheets a year) of plywood and this setup works very well. I surface the spoilboard before each cutting job making sure everything is nice and level. I then surface both sides of the sacrificial boards to make sure they are aligned with the spoilboard surface. For smaller projects, I use a 1" piece of MDO with T-tracks. I can mount the project material to the MDO board then it has held down on top of the spoilboard with the vacuum.

I know you are not using a vacuum system for hold down but I had this system in place before I installed my vacuum system and it worked great.

[EricSchimel]

I've loaded 800 lb. logs onto my 5x8 SB (with six legs) and seen no detectable deflection. You must have a weak machine.

Concrete is a miracle material. A product of the gods.

Do you have a picture of those 800 pound logs? I’d love to see how you got them under the gantry.

If you’re doing math, a concrete slab would be comfortably over 1000 pounds.

On early PRS machines with 4 legs the weight of the gantry alone can sag the X rails:

http://www.talkshopbot.com/forum/sho...rusion-sagging

Which is why I added mid legs to mine.

Given that you, me and the original poster have “weak” machines I don’t think concrete, steel or granite slabs are a good idea.

But what do I know? I thought science and engineers made concrete, not the gods

[coryatjohn]

Do you have a picture of those 800 pound logs? I’d love to see how you got them under the gantry.

Faced on both sides with a chainsaw, then loaded with an engine hoist into the machine. I have a 12" Z and with 14" clearance under a 3" flattening end mill.

Concrete originally was discovered by the Romans, exactly when isn't known but it includes a volcanic ash, a product of the gods so to speak. Roman concrete has lasted, in salt water, for 2,000 years. Modern concrete, created by scientists and engineers, pales by comparison.

[EricSchimel]

Faced on both sides with a chainsaw, then loaded with an engine hoist into the machine. I have a 12" Z and with 14" clearance under a 3" flattening end mill.

Concrete originally was discovered by the Romans, exactly when isn't known but it includes a volcanic ash, a product of the gods so to speak. Roman concrete has lasted, in salt water, for 2,000 years. Modern concrete, created by scientists and engineers, pales by comparison.

You’ve got quite the large engine hoist! One for lifting engines in large trucks? Most the them that are for the home shop are rated to two tons or less.

I’m curious if anyone else has tried concrete as a table surface (on a router). I’ve never seen a DIY build or form an OEM.

[MogulTx]

I would say that people are building 2" thick concrete slabs for countertops all the time. With chintzy cabinets underneath to support them. It is about area of support as much as stout members to support.

Logs: I have a number of davit cranes and a couple engine hoists in my shop. My primary engine hoist is capable of about a ton. That's more than double an 800# log. For my 5 x 10 I installed a hoist on a beam trolley at the end of the machine. I figured that an electric machine that I could hook onto the product to be lifted was best... I can lift off the truck bed or off my trailer. My trolley rail is welded to my iron beams in my ceiling, and runs from the roll up door to a few feet down the machine bed. I don't do logs- yet. I am thinking I will keep all the components from the upgrade and start planning a franken bot for that....