Improving my waste board stability and rigidity for harder cuts

I have an all steel CNC router, the table is a solid steel sheet, in top of that i made a waste board from a particle board with M8 inserts under arranged in a matrix

https://cdn.thingiverse.com/renders/...w_featured.jpg

That board is well screwed to the steel sheet and fixed in multiple points.
The problem now is the board starts to lift and is no longer flat, beside that if i try to clamp my holders with high torque, screw starts to push the wood up on that area (start to crack), so it don't have the rigidity to hold hard stuff. It may due the weak quality of particle board and the lower thickness of 14mm after surfaicing. It work great for wood and some low DOC aluminium so far, but if i push DOC on aluminium the holders will not have force to secure the piece, and because i don't want to crack the wasteboard puting more force on holders.

So i have two ideias which i like to ask if they are a good way to go or bad ideia.


1) Do a waste board from 20mm 6082-T6, and use threaded holes to secure the pieces in same way of the previous waste board
Problem here will be when do woodworking and bit touch the surface, which almost never happen because i use a Z probe which work verywell and bits almost never touch wasteboard even when i do full thick cut, still that could happen and ruin the bit. So here's my aditional step to improve solve this:

2) In top of 1) have another waste board of wood (Pine or MDF) with same hole configuration, so my M8 screws will screw on aluminium sheet and wood will be there only to protect the aluminium sheet and bits from broke, that way i will have both (better fixture rigidity and the soft wood as waste)

3) Redo waste board in a better wood, mdf or pine?

which approach will be best? Or if you have better ideia i'm open...

Glue two layers of 20mm MDF together, with t-nuts in the middle. Won't be as rigid as the aluminum, but will be much cheaper, and much better than what you have now.

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Originally Posted by ger21

Glue two layers of 20mm MDF together, with t-nuts in the middle. Won't be as rigid as the aluminum, but will be much cheaper, and much better than what you have now.

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Price is not a problem, sheets are cheap here. Due i want rigidity i think i will go for it.
Now what thickness should i go? I can choose from 10, 12, 15, 20, 25, etc... What thread depth i need to strong secure a M8? Lets say clamp a vise to it
Also should i surface the aluminium sheet or waste board or both?

Wood and composites tend to fail under too much stress, and you end up ripping out the threaded inserts, they are designed to be sacrificial. What you could do, is mount t track up and down, side to side. Make sure to recess it leaving enough material to surface it flat.

Particle board is also considerably less stable than MDF, and will warp far more easily than MDF under various temps and humidity.

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Originally Posted by ljvb

Wood and composites tend to fail under too much stress, and you end up ripping out the threaded inserts, they are designed to be sacrificial. What you could do, is mount t track up and down, side to side. Make sure to recess it leaving enough material to surface it flat.

Particle board is also considerably less stable than MDF, and will warp far more easily than MDF under various temps and humidity.

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The kind of nuts i'm using are the following:

https://ae01.alicdn.com/kf/HTB1UML7P...rcas-Cegas.jpg

They don't fail since they are traped, but wood are starting to fail under pressure.
Which is more stable, durable and hold more pressure? MDF or Pine?

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Originally Posted by sn4k3

The kind of nuts i'm using are the following:

https://ae01.alicdn.com/kf/HTB1UML7P...rcas-Cegas.jpg

They don't fail since they are traped, but wood are starting to fail under pressure.
Which is more stable, durable and hold more pressure? MDF or Pine?

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MDF is far more stable than almost all lumber stock. Pine is the absolute worst you could use. It is a soft wood, and will warp and expand/contract with even minor temp changes.

The reality is, MDF was made to be stable, however it does not handle moisture very well, most woods don't handle moisture, but MDF really sucks it up like a sponge, which will cause warpage.

BTW, that is what I meant when I said fail, the wood, not the threaded inserts. Wood will always fail over time, but it is sacrificial, and meant to be replaced, and resurfaced a few times.to keep it level with the cutters. If you use 3/4" MDF and recess T track a few mm below the top, you will get a few resurfacings out of it, and rather than all the pressure from whatever clamps or fixtures you are using being placed on a single nut and spot on the wood, it is distributed by the t track. Keep in mind, that because it is slightly recessed, there will be some pressure on the screws. You could surface the board, and install the T-Track level with the top, but then you will need to remove the T-Track everytime you want to resurface. With it of course being level, placing your workpiece over the t-track and clamping it down will give you more clamping pressure with very little on the spoiler board.

Thank you for explain.
That case i think i will go with my 1) & 2) Ideia, that way i can hard clamp stuff without the deformation from screw and i guess the aluminium sheet will last "forever". t-tracks i have the ideia if you apply much force it will deform the thin ceil and have height variations depending on pressure? Also i saw tables made all from t-tracks and when they apply force it lift the structure, maybe the cheap chinese machines?

You have any suggestion about the optional thickness of the aluminium sheet to go? My fixture screws are M8 (1.25mm pitch)

Here's my design, 50mm spacing between each fixture threaded hole, larger holes with a cap are for fix the aluminium sheet to the steel table. Then MDF will have same cuts without the larger holes, and will use some of the border holes to self fix to the aluminium, that way i think i will have a better rigid setup. About moisure, if i apply some coats of varnish on MDF will it help? Sometimes i use water mist with alu mill just to cooldown.

https://i.imgur.com/7LHElEK.png

i would probably say no less than 12 mm thick. you need enough material thickness so your cap screws are below the surface and enough thickness at the bottom of the counter bores to hold it down well. but all this depends on how solid the machine is to begin with. 12 mm of threads would be a decent amount of treads to hold what ever your clamping to the sub plate. the thicker you go the better but price factors into things at some point. and that is assuming your using 8 mm bolts to hold the aluminum plate to the steel base of the machine.

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Originally Posted by machinedude

i would probably say no less than 12 mm thick. you need enough material thickness so your cap screws are below the surface and enough thickness at the bottom of the counter bores to hold it down well. but all this depends on how solid the machine is to begin with. 12 mm of threads would be a decent amount of treads to hold what ever your clamping to the sub plate. the thicker you go the better but price factors into things at some point. and that is assuming your using 8 mm bolts to hold the aluminum plate to the steel base of the machine.

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I design the cap hole to be 10mm deep, that way it will accept both M8 button and cap heads with a margin of +/- 2mm for cap heads, so if i go 15mm, will have 5mm remaining to support the cap, otherwise with 20mm sheet i will have 10mm, so i guess go with 20mm should be optimal if cost not a problem?
About cost i have buy in past a "AW6082-T651 PLATE 20 MM 500X500" that costs 120 € final price with shipping, my usable area is about 595x900, so i expect something like 240 € +/- for that solid 20mm sheet. As this is more a investment and improvement i rather buy good and make it last than go cheaper and regret latter for a few bucks diference.

PS: steel base is about 8mm thick, just like every granty plate, machine photo:

https://i.imgur.com/C8pz694.jpg
https://i.imgur.com/eat7XQu.jpg

since it's a smaller machine i would go thicker too. i'm working on a 4' x 8' machine and plan on a 1" t slot top. by the time i buy the material and pay for tax and shipping i'm looking at close to $2000 but that for close to 650 lbs of aluminum. be thankful it's a smaller machine for your investment. the bigger they get the more costly they become :)

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Originally Posted by machinedude

since it's a smaller machine i would go thicker too. i'm working on a 4' x 8' machine and plan on a 1" t slot top. by the time i buy the material and pay for tax and shipping i'm looking at close to $2000 but that for close to 650 lbs of aluminum. be thankful it's a smaller machine for your investment. the bigger they get the more costly they become :)

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Yeah that's almost 9 to 10x my machine, it could cost you some big money but now you are enjoying more and maybe results in better work and pieces, and maybe it already pay off... So is not necessary a waste :)
The guys where i buy from, have blocks of 3070mm x 1120mm x 250mm, thats insane and i don't wana know the price xD Also 7071 and 7075 series but i think i'm good with 6082 (95 HB)

well with all the extra cost that goes with big it's no wonder i'm still building it almost a year after i started the project :) i would not want to see the price tag on a chunk of material that size either :) mine is bad enough as it is :) when it comes to paying for the stuff i wish i had a machine your size :)

with the small machines your probably better to get some kind of anti vibration pad and anchor it to the floor. that would probably help a lot if you have not done so yet. they just don't have the weight to let gravity do it by itself.

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Originally Posted by machinedude

well with all the extra cost that goes with big it's no wonder i'm still building it almost a year after i started the project :) i would not want to see the price tag on a chunk of material that size either :) mine is bad enough as it is :) when it comes to paying for the stuff i wish i had a machine your size :)

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Well you have one solution, do a machine of small size and your wish comes true ^^

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Originally Posted by machinedude

with the small machines your probably better to get some kind of anti vibration pad and anchor it to the floor. that would probably help a lot if you have not done so yet. they just don't have the weight to let gravity do it by itself.

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My machine is heavy due to steel content, is +/- 400kg as it is now, i can't move, shake or lift by my hand. It's not super rigid due construction and steel plates are welded at corner so you see the problem... Table is secured only in corner with a square frame, so center is unsupported, in future i want to put a grid of steel tubes under it. Non operation can move the machine and my weak stepper drivers can only shake X axis when using about 600mm/min accelaration and zig zag operations, but body stay in place. I also made a bench dedicated to the machine, it's not fixed into it, i placed a cardboard layer between table and machine and it have 3 heavy duty rubber feets per side. Each feet mean remove one screw from linear guide and use the feet instead. Don't know if i'm doing it correctly but since machine is there it not moved. Also i'm waiting for my new motor upgrade, Delta 400W AC Servos, that will make some damage! My 2000mm/min max speed hurt me when i have to go from one side to another, so the 15000 and 20 000mm/min will be usefull to me.

If you have any advice please feel free
Here fotos of actual machine and feets



https://i.imgur.com/ES3Xbgk.jpg
https://i.imgur.com/GqbQpHx.jpg
https://i.imgur.com/dPDNu4H.jpg