AVID PRO 4x9 build newbie advice

[TommyM]

After researching all kinds of suppliers and spending many hours reading forum posts, I've just put an AVID kit on order. I have decided to build my own support table from plywood and LVL beams rather than use their leg kit. I'm a retired structural engineer and believe I can build a more rigid and massive base than the aluminum offering and design it so I can store 4x8 sheet goods below the table. I'd appreciate any advice and experience anyone has to offer. I specifically wonder about the best way to attach the CNC table extrusions to my wood table base. If I don't get a rigid mount here, the mass and stiffness of the base will not be effective.

I was thinking of attaching standard aluminum angle to the extrusion with t-nuts and screwing the other leg of the angle to the plywood base as shown in the attached sketch. The length of the aluminum angle would be as long as possible (maybe 12" or so) with multiple fasteners. Obviously on the rails, I could only do this on the inside face since the drive mounts on the outside face. Any thoughts?

For general advice, I ran across a post on this forum from a few years ago titled, "PRO4896 - Things you wish you knew before you started". That was useful info. I'll summarize below. If you have additions, please post.

Thanks,
Tom



https://www.cnczone.com/forums/cnc-r...w-started.html

• loc-tite

o Regarding loctite, while it's not a bad idea, aluminum can act as it's own lockwasher. IE there is enough compression and give to the aluminum itself (in fact the slots on the 80/20 extrusion are specifically designed to be able to be pulled towards the fastener to help lock everything together... They call this the "2 degree drop lock" ). So assuming you tighten things down well enough, I don't expect loctite to be as useful as it is in other applications.

o When we built our Pro 48x48 this summer, we checked with CRP and they said no Loctite needed except for the setscrews on the pulleys for the belt drive. Blue of course, not red. We followed their advice, and just made sure we had each fastener good 'n tight. I thought CRP's instructions and support during the build were outstanding

o I asked the question, didn't get an answer from crp. I was wondering the optimal torque while building. That would have been a good piece of information.

• Run your electric where you want everything to be
• Spend as much time as you can leveling before moving on
• I over tightened my belts. Started hearing a click twice every revolution. They do not need to be that tight. About a 1/4 inch of deflection with your finger pressure should do. They work well surprisingly without much tightening at all.
• Torque check each fastener
• Think about dust collection hose and where it will run.
• You'll want to be able to 'walk around' the machine after it's set up, so don't put it in a corner up against the wall.
• When assembling the base, measure the spacing on the cross members VERY carefully and make it a nice even number for the center to center measurements on the T-slot, will make automating of spoiler board creation mucho easier (I have mine drill pilot holes for holds-downs that screw into the t-tracks in those cross members).
• When you're putting on the gantry risers, make sure they are "right side up". There are holes only one end. Don't ask why know this.
• I added a sliding shelf and a lift to the base before i enclose everything. Then i can easily store full sheets and Jack them up to the table level to slide on. Should increase storage in my shop and help with weight.
• I wish we would have done something nicer with our table design to protect the limit switches - we just added a 2x4 protruding out to serve as a barrier protecting the switch.
• Make sure you decide how to attach the extruded rails to the table.
• Make sure you don't take the plastic retainer out of the linear slides - it should get pushed out as you slide it on the rail. (As another poster said, dont ask me how I know this ).
• Use MDF sheet for top. Can drill holes wherever you want. Can cut into surface without worry. Then resurface when needed. Put in dog holes for dogs and clamps. I had a T slot table on previous machine. Wasn't as good as I thought it would be. Worried about cutting through. Had to use scraps as spoil boards. Was slippery and therefore clamps needed to be tighter.

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[peteeng]

Hi Tom - The construction extrusion suppliers sell cast angles, use those. Avid may have them on the shelf. They use them in their kits...Peter

Cast - 90 Degree Corner Bracket - Maker Store USA

[ubergeekseven]

Hi Tom - The construction extrusion suppliers sell cast angles, use those. Avid may have them on the shelf. They use them in their kits...Peter

Cast - 90 Degree Corner Bracket - Maker Store USA

You'll notice that the extrusions are sent directly from 8020, might as well go to the or their eBay store. You can get great deals on random stuff from them on eBay. Usually cheaper if there color was not exactly right or a ding on the surface. Nothing structurally wrong.

I'd like to see that storage shed that pulls out and jacks up to the table surface of anyone knows of pictures.

Sent from my SM-N960U using Tapatalk

[hanermo]

Em..
Politely, it will be useful to look at commercial machines and what they use.

The general rule of thumb is that machine tools need to be 50x stronger than their max stressed load.
So *rigid* means that a lathe bed than has 100 kgf max force applied (about 14 mm ballscrew) needs to have a breaking strength around 50 x 100 = 5000 kgf.

Every single good lathe / mill produced has about the same ratio. +/-, ballpark.
Give or take.
So any modern lathe or mill (or old lathe or mill) will have about a 32-40-50 mm ballscrew, 1200 kgf of force upwards, but the mechanicals will be 50x "stronger" than the ballscrew thrust.

My cnc mill (VMC scratch built) has 50 metric tons theoretical load carrying capacity, in the z axis, 12 trucks of 35 mm hiwin hgr/hgw, some with high preload.
6 rails.
I expect to ever only use about 500 kgf force, with a 32 mm / 5 mm ballscrew, under 50% of rated load for the screw.

Rigidity is hard to achieve, and You need about 50x more than you think.

My own example is only to illustrate what I mean, scale as appropriate.
Look at optical tables for real rigidity, by mass/volume.

You want somewhere around 40 N/um rigidity, 10-100 range, for routers/mills.
Plenty of pdfs online.