[nevermnd]

Hey guys,

So I am more on the EE side of these things, but have already received a lot of really good advice here thus far.

Unfortunately I can't do cast, which might be best, but I am trying to build out/design my gantry design.

Thus, with steel, am I better off looking at a carbon steel or some sort of 'mild steel' alloy? And, especially with the second choice, there are so many options: (4140A, 4140H, 8620, 4340, 52100, etc).

Obviously with my design I am not looking to produce parts for NASA or something (or that level of spec),
but some input on material choice would definitely help.

Thanks.

[peteeng]

Hi Never- Any grade or alloy of steel is fine. You are looking for material stiffness and all steels have a very similar young's modulus. Then you get the cheapest steel for the size you want. Peter

[nevermnd]

Hey thanks-- yes 'Young's modulus' does now come back to mind, but good to know anything I work with will be 'okay'. I kind of worried the carbon steel might be 'too rigid'.

[ardenum2]

it might be 'too rusty', I had to throw away a few good pans and knives over the years.

by the way, there's never 'too rigid' with machine tools. If you know of a TPa material let me know

[joeavaerage]

Hi,
peteeng is right, any steel will do.

You could go to the trouble and expense of using hardened and tempered 4340, but it would be exactly the same stiffness as a the same part made in mild steel. Sure
the 4340 would be way stronger but we never come within a fraction of 1% of the strength....its all about stiffness.

Mild steel is obviously way cheaper than 4340 but more importantly can be welded without problem. When steel is welded it really needs Thermal Stress Relief (TSR)post welding, otherwise it will
move months and years later, especially if its machined. Vibratory Stress Relief is a much cheaper alternative and works OK in many situations, but TSR is still
the gold standard. TSR is not cheap!

May I suggest find out whom the heat treaters are in you area, and especially what size oven they have.

As an example when I was building my mill the only local heat treater's oven was 700mm long, ergo my axis bed castings are 695mm long. It cost $6NZD/kg....and that was prior to COVID!
You NEED to find out what capability you have access to and what its going to cost before you make any plans or you could face an unanticipated budget hurdle which will screw your
project.

My machine is steel and cast iron......both inclined to rust, but aside from a little surface discolouring it does not, I'm guessing the water soluble oil in the coolant, and I use flood coolant
a lot, inhibits the rust. All-in-all I'd say rust is a non issue, having the means to make full penetration welds and subsequent TSR are what you need to concentrate on.

Craig

[peteeng]

Hi Craig - Look up Fullerenes and nanotubes they are above 1TPa stiffness. Peter

https://en.wikipedia.org/wiki/Mechan...rbon_nanotubes

[joeavaerage]

Hi,
I have read up on them before....but where can you get them? My understanding is that like Bucky Balls they are pretty much a vanishing small by product of various chemical processes
of carbon. Whatever they may be or whatever potential they may have they are true 'pie in the sky' stuff for me.

Craig

PS: I guess its entirely possible if and when I burn the toast that a small fraction ends up as carbon nanotubes, they might be stiff but I'm not at all sure
they taste any good!

[peteeng]

Hi Craig - There are commercial suppliers of these things. Not quite 1TPa yet but getting there. They are used as additives in resins and paints to do various things. Sheet material is available as well. But highly expensive, used by the military and aerospace at the moment, will filter down to commercial level eventually. The custom bike maker I do stuff for uses a nanoparticle interlayer in some of his CF tubes. He gets the interlayer from switzerland. Its 0.025mm thick and does make the tubes stiffer. Weve had tubes tested... Peter

heres a list of suppliers - haven't looked at them just a search

Top Fullerene companies | VentureRadar

do you have a blender?
https://www.newscientist.com/article...20atom%20thick.

[nevermnd]

Dear Joe,

So you are the one that set me on the right direction in that 'welding the whole thing' would not be a wise decision.

However, for the cross bar of the gantry I have been thinking a bar channel design to hide/cover/carry the ball screw-- And I figure to get it to mount to the sides of the gantry I *have* to weld some mounting plates on there on the side... Or how else is this going to work ? (Or, I suppose make angle brackets adjacent to it, so *everything* is defined by a fixture-- I also worry about this solution a bit because while vibration is the enemy of a CNC, it happens and, little by little, it is going to shake the bolts lose over time)

Just curious if you had any other thoughts (?)

However,

Hi,
peteeng is right, any steel will do.

You could go to the trouble and expense of using hardened and tempered 4340, but it would be exactly the same stiffness as a the same part made in mild steel. Sure
the 4340 would be way stronger but we never come within a fraction of 1% of the strength....its all about stiffness.

Mild steel is obviously way cheaper than 4340 but more importantly can be welded without problem. When steel is welded it really needs Thermal Stress Relief (TSR)post welding, otherwise it will
move months and years later, especially if its machined. Vibratory Stress Relief is a much cheaper alternative and works OK in many situations, but TSR is still
the gold standard. TSR is not cheap!

May I suggest find out whom the heat treaters are in you area, and especially what size oven they have.

As an example when I was building my mill the only local heat treater's oven was 700mm long, ergo my axis bed castings are 695mm long. It cost $6NZD/kg....and that was prior to COVID!
You NEED to find out what capability you have access to and what its going to cost before you make any plans or you could face an unanticipated budget hurdle which will screw your
project.

My machine is steel and cast iron......both inclined to rust, but aside from a little surface discolouring it does not, I'm guessing the water soluble oil in the coolant, and I use flood coolant
a lot, inhibits the rust. All-in-all I'd say rust is a non issue, having the means to make full penetration welds and subsequent TSR are what you need to concentrate on.

Craig

[peteeng]

Hi NM - Bolts will not come loose if correctly torqued and if you use loctite... Bolts come loose when stretched in use and cnc machines do not place enough strain on bolts for this to occur. A fully bolted construction is a very damp and stiff structure when done correctly. Welding is a can of worms unless you can thermally stress relieve the structure. If your into oxy actylene then brazing or braze welding is a worthwhile approach. Does not need TSR and you can't anyway as TSR temp is above the bronzes melting point (red heat +650deg C) so the assembly would fall apart. Peter

[joeavaerage]

Hi,

So you are the one that set me on the right direction in that 'welding the whole thing' would not be a wise decision.

I never said welding was a bad idea, but that you need to TSR afterwards. TSR is not magic or voodoo, there are plenty of places that do it, roll up your sleeves and find some. Then you'll know
whether it viable or not.

I don't know why it is that whenever TSR is recommended hobbyists 'shy away like you've just threatened to rape their mother'. If you refuse to consider it then welded steel is off the list, and welded
steel is humanities strongest, stiffest, most versatile construction method, and for the strength and stiffness the cheapest as well. You want to take that off the list?

Craig

[ardenum2]

Hi NM - Bolts will not come loose if correctly torqued and if you use loctite... Bolts come loose when stretched in use and cnc machines do not place enough strain on bolts for this to occur. A fully bolted construction is a very damp and stiff structure when done correctly. Welding is a can of worms unless you can thermally stress relieve the structure. If your into oxy actylene then brazing or braze welding is a worthwhile approach. Does not need TSR and you can't anyway as TSR temp is above the bronzes melting point (red heat +650deg C) so the assembly would fall apart. Peter

think we talked about this before but what kind of joint shear strength are we talking about with brazing?

[Lilia]

Hello, dear
About carbon steel, I think I can recommend you a supplier.
https://wzppgi.com/ This is the website.

[Mr-MaW]

Very coincidentally, I have just finished the base of a gantry machining center.
What kind of gantry do you need? How much is the trip? What materials are processed?
You can take a look at the photos of my products.

Of course, if you need to find carbon steel materials, or welded finished products, I can also help you find the right supplier.

[Mr-MaW]

This beam is made of cast iron, and I also made a lot of welded beams. The base is made of marble mineral casting.

[ardenum2]

This beam is made of cast iron, and I also made a lot of welded beams. The base is made of marble mineral casting.

which foundry do you use for the iron cast?

[Mr-MaW]

This beam is made of cast iron, and I also made a lot of welded beams. The base is made of marble mineral casting.

po

[Mr-MaW]

which foundry do you use for the iron cast?

There are many foundries in China, and I would have had my own foundry as well. For environmental reasons, our company started the production of mineral castings.