First Build-Steel Gantry CNC - Comments on design wanted

[njhussey]

Welcome to the forum Olaff!! This is one of the most thought out researched and designed starts to a build log I've seen for a while.

Looking good, as Clive and Boyan said the Z looks a little flimsy and could do with some bracing/stiffening if you're going to use steel. I can't help thinking that a couple of lumps of 20mm Aluminium tooling plate with milled (you say you have a manual mill) recesses for the ballscrew and carriages would be a simpler option and you wouldn't have to worry about distorting the front plate welding the rail supports on....just a thought.

[olaff]

Hi all and thanks for your comments.

I suspected as much that the Z axis was the weak link.
I have had quite a few variations of the design that whas more stiff, but got to concerned about weight and scrapped the ideas. Then I started to think about Aluminium instead...

When it comes to the motors, I choose the closed loop steppers mainly to prevent racking on the X axis. (since im a beginner at this, its one of the main concerns)... It was not so much info to find on the net, but found some people that was very satisfied with this type of motors. I negotiated quite a good price for the set of motors and drivers, so I decided to just go for it. I understand that this still is just a stepper, but hope it will work good on this type of machine.

A few more questions as im not so familiar with aluminium
-Do I have to use Aluminium Tooling plate, or would 20mm 5083 Aluminium be OK? (Plate used in ship building industry)
-Does using Alu plate still require additional bracing of the Z axis, or is this much stiffer in it self?

I will have to work a bit more on the design of the Z axis, and I guess finally make a descision on Steel or Alu.

[njhussey]

A few more questions as im not so familiar with aluminium
-Do I have to use Aluminium Tooling plate, or would 20mm 5083 Aluminium be OK? (Plate used in ship building industry)
-Does using Alu plate still require additional bracing of the Z axis, or is this much stiffer in it self?

Tooling plate is best as it is ground flat so you don't have to do as much machining. With standard Aluminium plate it's not quite flat so wound need machining so the rails were exactly level with eachother. No Aluminium plate if it's 20mm thick wouldn't need additional bracing, there are loads of examples on this forum of machines with exactly this. I wouldn't get hung up on weight as I've got a 40mm thick front plate hanging off my Z axis and it's no bother at all. As I said somewhere else when I was putting my 20mm thick aluminium plate on the base I had my machine vertical and just for a laugh stood on the gantry and turned the X axis ballscrew (both linked with a belt) pulley with a thumb and two fingers and easily lifted my weight (19.5 stone) so don't get too hung up on weight, there's a huge mechanical advantage when using ballscrews!!

I will have to work a bit more on the design of the Z axis, and I guess finally make a descision on Steel or Alu.

Looking forward to seeing your new design....

[Boyan Silyavski]

As far as the Z plate/s its very simple . Steel is 3 times stronger than aluminum, 3 times cheaper and it takes 3 times the time to make it as you have to paint it.

So as i see it the best would be aluminum plate/s with bolted steel braces at the sides for reinforcements.

[JAZZCNC]

As far as the Z plate/s its very simple . Steel is 3 times stronger than aluminum, 3 times cheaper and it takes 3 times the time to make it as you have to paint it.

Lets compare Apples with Apples here.!!. . . . It's not 3 times cheaper if you buy high grade Cast Ground Steel tooling plate.!!

If builder doesn't have the abilty to machine steel flat then they are in for a world of pain when it comes to accurecy.!

Weight should be a Concern but only in certain cutting conditions. If you require high positional feeds with high velocity direction changes then 90Kg is getting close to stressing steppers. Cutting material like aluminium won't be a problem has the feed rates are low but cutting materials like Mdf etc do require higher feedrates to cut correctly so if your cutting shapes that have high velocity direction changes this is where heavy gantry will show up.
That doesn't mean it will cause you problems and you can't cut these materials but it will mean cutting at lower feeds than could be achieved with motors better suited to the weight. It also lowers tool life and finish quality if your cutting lower than optimum feeds.!

It's like Mr "N" says " Every action as equal and opposite re-action" So heavy means slower or more power.! Cut below optimum means Wear tools quicker.!

Regards the Aluminium Bed then I wouldn't bother if i'm honest. Even when cutting aluminium for anything other than real accurate work (or when requireing flood coolant) then you'll use some kind of Spoil board under the material, often Mdf or Ply, so it's wasted money really.
I wouldn't even go to the trouble of building a torsion box if the frame is strong, which it is.? Some form of stable material like high grade ply wood for a base is all that's needed. Then on top of this have sacrificial board that you surface flat. Even if you go to the trouble of making a torsion box you'll still use a sacrificial board which needs surfacing so you gain nothing over just normal piece of Ply.

Put Matrix of threaded inserts into the lower ply and you have hold down system.

[GEOFFREY]

Hey Jazz, I left school in 1958, but I seem to remember that it wasn't mr."E", but mr. Newton who said that!!!

(one of his laws of motion I think. I am now diving for cover!!!). G.

[JAZZCNC]

Hey Jazz, I left school in 1958, but I seem to remember that it wasn't mr."E", but mr. Newton who said that!!!

(one of his laws of motion I think. I am now diving for cover!!!). G.

Ahh ahh well I didn't go to school much so that explains that. . . Better get it changed quick before anyone see's it and Don't tell Clive else he'll take the Piss for ever. .

[olaff]

Lets compare Apples with Apples here.!!. . . . It's not 3 times cheaper if you buy high grade Cast Ground Steel tooling plate.!!

If builder doesn't have the abilty to machine steel flat then they are in for a world of pain when it comes to accurecy.!

Weight should be a Concern but only in certain cutting conditions. If you require high positional feeds with high velocity direction changes then 90Kg is getting close to stressing steppers. Cutting material like aluminium won't be a problem has the feed rates are low but cutting materials like Mdf etc do require higher feedrates to cut correctly so if your cutting shapes that have high velocity direction changes this is where heavy gantry will show up.
That doesn't mean it will cause you problems and you can't cut these materials but it will mean cutting at lower feeds than could be achieved with motors better suited to the weight. It also lowers tool life and finish quality if your cutting lower than optimum feeds.!

It's like Mr "N" says " Every action as equal and opposite re-action" So heavy means slower or more power.! Cut below optimum means Wear tools quicker.!

Regards the Aluminium Bed then I wouldn't bother if i'm honest. Even when cutting aluminium for anything other than real accurate work (or when requireing flood coolant) then you'll use some kind of Spoil board under the material, often Mdf or Ply, so it's wasted money really.
I wouldn't even go to the trouble of building a torsion box if the frame is strong, which it is.? Some form of stable material like high grade ply wood for a base is all that's needed. Then on top of this have sacrificial board that you surface flat. Even if you go to the trouble of making a torsion box you'll still use a sacrificial board which needs surfacing so you gain nothing over just normal piece of Ply.

Put Matrix of threaded inserts into the lower ply and you have hold down system.

Hi Jazz. Thanks for your comment.

I have done a quick calculation and find that using 20mm Aluminium in the Z could save me somwhere in between 6-8kgs...Its not a lot, but i guess every kg helps. I was of course hoping to be able to use the appropriate feedrate for the different materials...Will it help to gear the X axis different? I was thinking 1/1, but that can be changed.

The biggest problem seems to be that I cant find anyone that sells tooling plate in this country....So I guess i will have to go with 5083 plate if I decide to go for aluminium, and build myself a flycutter for the mill and see if i can get it flat..

Yes I guess I drop the idea about Alminium bed and use mist cooling if needed. The Torsion box idea is that its quick and easy to remove in case I need the full height. The plan was to have treaded inserts in both the torsionbox and on the lower plate that sits directly on the bed.