Advice on Mammoth CNC Router Build - Steel Framed - 2440mm x 1220mm cutting area!

[EddyCurrent]

Ok I will spend some time converting it all to 80mm box, what wall thickness would you recommend?

I would say 5mm, it's quite heavy but if you are attaching rails directly to it then you need some thickness for the screw threads. I used 3mm box so I'm having to glue a piece of 6mm flat strap inside to give it a 9mm thickness. The best way I've found to decide on material thickness for threads is to see what thickness a nut is for any particular size bolt and use that as the minimum.

[mekanik]

Hi M8
with such a large machine i think resonance could be an issue, i think Jazz commented on another build and suggested loosing the symetry of the supporting members, i am sure he will comment shortly.
regards
Mike

[Wejjmeister]

Hi M8
with such a large machine i think resonance could be an issue, i think Jazz commented on another build and suggested loosing the symetry of the supporting members, i am sure he will comment shortly.
regards
Mike

Hi Mek,

I considered this whilst planning it all, all boxed sections in the side of the frame would be filled with sand, and then the holes plugged afterwards, including the diagonal braces, would this be enough to damp the resonance?

[mekanik]

Hi
I am a new to this game and was just passing on information i have picked up from the forum, Jazz uses sand filled sections, for a definitive answer you might be better waiting for advice from our senior members that have actually built and used a machine(hint)
Regards
Mike

[Wejjmeister]

Epoxy I think although I will also be taking a leaf from Jazz and making it so the 3m lengths can be shimmed to give a better starting point, then on with the epoxy!! Funtimes!

So to clarify, I can mount HiWins as in the initial design i.e on top of the rails.

Jonathan, can I trouble you to expand on the disadvantages??

Thanks guys!

[Lee Roberts]

Epoxy I think although I will also be taking a leaf from Jazz and making it so the 3m lengths can be shimmed to give a better starting point, then on with the epoxy!! Funtimes!

So to clarify, I can mount HiWins as in the initial design i.e on top of the rails.

Jonathan, can I trouble you to expand on the disadvantages??

Thanks guys!

I don’t know if I’ve misunderstood Jazz here or you with regards to shimming...

Surly enough accuracy can be achieved when cutting and then wielding the frame that any small differences would be "levelled" out from doing an epoxy bed for the rails to then sit on?

To confirm, what it sounds like your suggesting is, having the ability to “shim” the 3m lengths, along their lengths.

.Me

[EddyCurrent]

I don’t know if I’ve misunderstood Jazz here or you with regards to shimming...

Surly enough accuracy can be achieved when cutting and then wielding the frame that any small differences would be "levelled" out from doing an epoxy bed for the rails to then sit on?

To confirm, what it sounds like your suggesting is, having the ability to “shim” the 3m lengths, along their lengths.

.Me

That's the method I'm also using and I found that after welding, one corner of the frame was 3mm out of level with the other. This might be regarded as too much depth for epoxy treatment alone. I don't know for sure ? but at least I can shim the rails to as near level as possible then use epoxy from there.

[Clive S]

That's the method I'm also using and I found that after welding, one corner of the frame was 3mm out of level with the other. This might be regarded as too much depth for epoxy treatment alone. I don't know for sure ? but at least I can shim the rails to as near level as possible then use epoxy from there.

Eddy You might have seen this before there is no problem with the thickness of the epoxy Jonathan and I have used it I think Dean uses some sort of epoxy putty which is stiffer, he has explained that on other threads.

I poured this to about 5mm deep it is very slow setting 10 - 20 hours and don't touch it for 48 hours. Wests system
..Clive

[Lee Roberts]

That's the method I'm also using and I found that after welding, one corner of the frame was 3mm out of level with the other. This might be regarded as too much depth for epoxy treatment alone. I don't know for sure ? but at least I can shim the rails to as near level as possible then use epoxy from there.

Thanks Eddy, any idea why this happened or?

Eddy You might have seen this before there is no problem with the thickness of the epoxy Jonathan and I have used it I think Dean uses some sort of epoxy putty which is stiffer, he has explained that on other threads.

I poured this to about 5mm deep it is very slow setting 10 - 20 hours and don't touch it for 48 hours. Wests system
..Clive

Hi Clive, in your picture to make your epoxy "gutters" you look to have used MDF, i dont know if you've seen Jonathan's recent machine but he made his using aluminum and then left those in place once the machine was ready. My question is, what are the edges like on the epoxy once it "sets", i.e dose it need protecting from damage and so on to keep it together.

Did you do anything to yours after the machine was ready to be used to keep it safe?

I tend to agree - there becomes a point when an extra couple of mm of epoxy doesn't cost much compared to the added material/time required to get the frame more accurate. The epoxy is pretty strong/hard and the damping properties may be useful, so I wouldn't be too concerned about minimizing the thickness, within reason. If you look in my build log the epoxy is quite thick, but don't treat that build log as gospel - there's plenty of room for improvement.

Thanks JB, I didnt see your post untill i posted mine.

.Me

[Jonathan]

expand on the disadvantages??

If the rails are on the bottom surface then the bearings, i.e. your supporting points, are closer to the tool/bed. The overhang is therefore reduced, so the stiffness is correspondingly higher. It does however make mounting them on epoxy more challenging - although you could conceivably mount the Y rails and X bearing blocks on the same epoxy leveled surface and get very good accuracy. I'd try drawing both orientations and see which looks the most promising.

Surly enough accuracy can be achieved when cutting and then wielding the frame that any small differences would be "levelled" out from doing an epoxy bed for the rails to then sit on?

I tend to agree - there becomes a point when an extra couple of mm of epoxy doesn't cost much compared to the added material/time required to get the frame more accurate. The epoxy is pretty strong/hard and the damping properties may be useful, so I wouldn't be too concerned about minimizing the thickness, within reason. If you look in my build log the epoxy is quite thick, but don't treat that build log as gospel - there's plenty of room for improvement.