ShopBot Table expansion

All,

I have gotten some components from ShopBot and am widening my table from a 5' to a 6' table. I will now have a 6' x 10' layout.

What I could use some suggestions on is how to set up the underlayment and the spoilboard. The largest sheets of plywood I can get locally are going to either be 5 x 5' in Baltic Birch, or 4 x 8' in standard ply materials. Anyone know of anything else available for the first layer???

Plenum:I don't use vacuum, so I don't have to plan for that. However, for stability purposes, I probably want to run a three layer stack. so I am still thinking two layers on top of the base layer.

Locally I can get MDF in 5' x 10', so I could potentially lay a 5' x 10' and a 1' x 10' to get a complete layer, and then flip the orientation for the next layer's seam to the other side of the table, so that the seams do not occur in the same line.

Alternately, I could start with 4 x 8' sheets and orient them long-dimension across the end of the machine (6' width), and use two 4'x6' sheet sections and a 2' x 6' section to reach the full 6 x 10, and then probably use the 5 x 10' MDF layers as described above to make my bed and spoilboard scheme.

Do any of you wise ones have an alternate idea on this?

Thanks for your thought on this.

Monty

If you have the Z, you could pour a 3" concrete layer. That would provide the absolute most stable base with zero flex. It would also weigh about a ton (~25 80 lb bags) or so which would also make the table a lot more stable. On top of the concrete, MDF. You could even run a surfacing routine on the concrete surface in the first 24 hours after pouring as the concrete would be soft enough to machine easily at that point. If it was me, I'd rig a float on the spindle and run a surfacing routine before the concrete set to make it as level and flat as possible.

I know, rather bizarre but for such a big table, probably work great.

I used MDO for my base layers… Medium density overlay is a sealed, primed product, not as susceptible to shrinking or swelling in our Texas humidity/temperature changes!

For my spoil board I like to use a moisture resistant MDF like Exteria or Medex for the same reasons. If your shop is fully temperature/humidity controlled 24/7, movement of these materials may not be an issue.

These materials aren’t big box items, but cabinet shop supply houses like “The Plywood Company” have them, often in 5’ X 12’. Split a sheet of this to get 2- 5’ x 6’ pcs.

SG

Excellent suggestions, Gents. Thank you for your input!

Monty

Rats. Local cabinet shop supplier tells me that they can't get 5 x 12, and that they are out of 5 x 10- and will be "months" getting more... I may be into forming up a box and pouring!

I would not do concrete. That's insanity. You'd never ever be able to move that machine again. You'd likely warp the cross members and crack the slab anyway. The long X rails can sag under the weight of just a standard table setup if you have one of the old 4 legged ShopBots, I'd guess they'd buckle under the weight of concrete or granite.

I haven't done every single table configuration (far from it) but I've been pretty happy using sealed MDF, and now two layers of Extira (base solid, plenum second layer, LDF top layer) and that's been nice and stable, more than my old setup which was Plywood base, MDF, LDF. But even that setup was pretty good, it just needed resurfacing when there was a wild moisture swing.

I'd recommend going one of those routes. You can cut down 4x8s and biscuit them together to make whatever size you need for short money. If you're feeling spendy and you want something super stable look at a phenolic top. Very stable but only as stable as what you put it on. I looked into that once and it was going to be $700 to $1000 just for the sheet, not to mention the extra cross members I'd need to support it.

If they had a rigid panel in the size I want, I would pay money for it - but it would need to be a full 6 x 10, so I could do it in one sheet (if I have to get spendy)... Concrete might be heavy, but the new kit from SHopBot is going to be well supported. And I have upgraded leveling feet and done some other mods. Not concerned about the structure nor the slab! (I have an 18" thick granite block that would be just about perfect, if I could figure out how to slave the rails to it! That weighs in at about 30K pounds, but is flat to a few thousandths across the face! I have found some sheets of MDF, and need to source some good underlayment... working on it...

I have upgraded my legs too... Trust me don't put concrete or granite there. Just biscuit some panels together and you'll be in great shape.

Quote:

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Originally Posted by EricSchimel

I would not do concrete. That's insanity. You'd never ever be able to move that machine again. You'd likely warp the cross members and crack the slab anyway. The long X rails can sag under the weight of just a standard table setup if you have one of the old 4 legged ShopBots, I'd guess they'd buckle under the weight of concrete or granite.

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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.

I have 12" indexer envy... I dream of building a custom machine just to do large/long columns...

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.

Quote:

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Originally Posted by coryatjohn

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.

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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 ;)

Quote:

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Originally Posted by EricSchimel

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

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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.

Quote:

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Originally Posted by coryatjohn

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.

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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.

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....