Bridge Gantry Profile

[~andy]

Do you reckon the profile below has what it takes to be the gantry on wood router?

10398

Profile rails on the front face, ball screw in the middle.

Very expensive, but very simple.

[EddyCurrent]

I was going for this design myself but changed to the L shape using 100x50 aluminium box section. Have you seen this calculator ? it might answer your question, I'm not sure if this is the most up to date version of it though.
http://www.mycncuk.com/forums/linear-rotary-motion/2214-cnc-machine-stiffness-calculator.html

[johnsattuk]

Could you give some details - manufacturer/supplier, cost ?

I like the look of this section

[~andy]

Take a seat.



It's a Maytec profile about ~£130 a meter.

Oh, you'll need an M14 tap on top of that cost.

[asbo]

Don't do it :concern:

I got over 10 meters of steel box section cut to length and delivered for less than that, and that could probably be had cheaper elsewhere. Probably harder to work with, but 10x cheaper :thumsup:

[johnsattuk]

Maybe a bit expensive but would make a nice neat job, would be good for mounting the "X" rails as well.

Have M14 taps. :thumsup:

[JAZZCNC]

Do you reckon the profile below has what it takes to be the gantry on wood router?

10398

Profile rails on the front face, ball screw in the middle.

Very expensive, but very simple.

Don't waste your money is my answer.!! . . . . . What width Gantry do you want.?

Because I can tell you with 100% certainty thru building several machines with the L shape gantry using 45x90 profile that it is more than capable of handling cutting wood at 4' width and that's with using tall style gantry sides not sat direct on bearings like I do for machines mostly cutting harder materials.
On the narrower machines I've built with 700mm cutting width so 900mm wide gantry and tall style gantry sides it handles cutting aluminium no problem at lower DOC.

From KJN it's £25mtr and another bonus is the 45mm slot spacing fits the BK/BF bearing holes so easy fastening of ballscrews.

Also agree that Steel is much cheaper and I use it all the time but also see the Profile appeal for ease of building and neatness. For a wood router it works very very well and more than strong enough.

[~andy]

Don't waste your money is my answer.!! . . . . . What width Gantry do you want.?

1m total length, 600mm travel. This does allow for a very tidy set up, the stepper directly coupled in c channel and simple Z plate.

[JAZZCNC]

1m total length, 600mm travel. This does allow for a very tidy set up, the stepper directly coupled in c channel and simple Z plate.

I wouldn't use that stuff got to many . . . It's.!!

It's light duty thin wall stuff.
It's too narrow in middle with potential to twist.
It doesn't provide ideal or easy rail fastening because slots are in wrong places.
It will fill with and collect chips if plan is to face forwards, (say this because of your simple Z plate ref.?)
It won't allow for simple Z plate if rear facing has the top of channel restricts access to ballscrew so placing ballnut bracket further back than needed.
It's not going to provide anything extra the L shape does.
It's going to cost 3 times the price of L shape.
It's going to be weaker than L shape has it's thin walled and narrower.

Bottom line is It's inferior and 3 x the price.!!! . . So why bother.!

[~andy]

Not fussed about the cost of the profile, if it provides an easy build. I've seen this profile with rails on the front and the screw in the middle.

It would be for a wood router so collection of chips shouldn't be an issue as 90% of the waste will be sucked away.

Just wondered if it was up to the job from a technical perspective (ignoring better/cheaper designs). I don't have the knowledge to say if the figures on the drawing are are acceptable for the purpose or how they compare.

[JAZZCNC]

Just wondered if it was up to the job from a technical perspective (ignoring better/cheaper designs).

Well If you have too much money then go for it.! . . It will work that's for sure but it would be a dumb thing ignoring better cheaper design don't you think.?

Problem with this stuff thou other than cost is it's light duty thin wall stuff so could resonate or twist/flex in longer lengths. It won't allow much easier build because there's more Drilling and tapping involved because the slots don't allow easy ballscrew mounting. Drilling and tapping profile is a pain on thick walled stuff but this thin walled stuff is rubbish for tapping and holding threads.

Also don't think just because you have vacuum that the shelf won't collect enough chips and fine dust to be a pain.!! . . . It will collect very quickly esp on material like MDF that produces fine dust. . .You'll need a very good Vacuum and dust shoe to contain every thing.

Personally I don't see the point of using this stuff has it's not really making anything easier costing 3 x times the price and is inferior in strength.!

[John McNamara]

Hi

Steel is three times stiffer than aluminium and for machinery stiffness is more important than strength in most cases. Any sort of deflection will add to the "Error budget" for the machine. Remembering that (Among others) the sum of all errors for misalignment, frame deflection, bearing slop and temperature have to be added together to calculate the maximum error.

Google search compare Steel to Aluminium: https://www.google.com.au/?gws_rd=cr&ei=2KNXUpy8Hsq6lQXxtIHADA#q=stiffness+steel+compar ed+aluminium

Regards
John

[~andy]

Well If you have too much money then go for it.! . . It will work that's for sure but it would be a dumb thing ignoring better cheaper design don't you think.

I'm not ignoring a different designs outright. Just looking at the options.


Problem with this stuff thou other than cost is it's light duty thin wall stuff so could resonate or twist/flex in longer lengths.

I can't tell with extrusion, and I don't know enough to be comparing section modulus and moment of inertia figures over other designs. It's a very strong cable tray really after all.


It won't allow much easier build because there's more Drilling and tapping involved because the slots don't allow easy ballscrew mounting. Drilling and tapping profile is a pain on thick walled stuff but this thin walled stuff is rubbish for tapping and holding threads.

I was thinking of drilling and tapping to a plate, and mounting off that to get the correct height.

[JAZZCNC]

I was thinking of drilling and tapping to a plate, and mounting off that to get the correct height.

I understand your thinking and desire to makes things that bit easier if your time or equipment challenged and i'm not trying to put youoff profile or push you into any particular design but the point I'm trying to push is if you must use this Profile for time and tool reasons then you won't save any work over the L design that uses Profile costing third the price. You will actually create more work and less strength/stiffness.

I use both steel and profile and like my comments before I know 100% the L design along with profile works perfectly for the application of cutting light to Medium hardness materials. Steel would be my first choice every time if heavier duty machine required or Budget was limited has it's simply the best way to achieve both. It's just time intensive compared to profile and needs more equipment/skills to work.

Like John says there's much more to successful machine than material strength and I can tell you for sure building a machine with the mindset of compromising machine strength or design in favour of easy building is recipe for a under performing machine.!

[EddyCurrent]

~andy, I too explored several designs and went from one to the other then back again, this was after much deliberation regarding ease of build and mainly a good sturdy design with cost being somewhat secondary. I therefore came back to the L design and 'borrowed' a lot of the ideas from Matt's build, http://www.mycncuk.com/forums/router-build-logs/6530-machine-month.html.
One advantage I like with this design is the lack of gantry sides which you will need in your proposal, although on mine I made add some triangulation here for added strength.

If you still want to go the extrusion route these are some links I found while researching that.

http://www.extrusions-aluminium.co.uk/Aluminium-Extrusions.html
http://aluminium-profile.co.uk/
http://www.valuframe.co.uk/
http://www.motedis.co.uk/shop/Slot-profiles:::1.html
http://www.metallin.co.uk/shop/
http://www.8020cnc.com/
http://www.boldman.co.uk/aluminium-profile-system/
http://www.damencnc.com/en/components/aluminium-profiles
http://www.zappautomation.co.uk/en/6-aluminium-extrusions

[~andy]

~andy, I too explored several designs and went from one to the other then back again, this was after much deliberation regarding ease of build and mainly a good sturdy design with cost being somewhat secondary. I therefore came back to the L design and 'borrowed' a lot of the ideas from Matt's build

Truth be told, I think that this is a great design with simple materials. One I've studied many times.

I think I've browsed most of those extrusion sites!

[EddyCurrent]

Well you seem to have made your mind up from the outset and the reality is it will most likely do your job so go ahead.

[~andy]

No. Not at all just exploring options. The base will be extrusion for sure, plate for the Z. Not fussed about the gantry, I just want something that is straight forward and easy to build.

Thought someone might have used that profile, or might be able to tell me how the numbers compare.

[EddyCurrent]

Did you look at that stiffness spreadsheet ?, at first I thought extrusion was not included but I found it in version 7 of the spreadsheet

[Boyan Silyavski]

No offence but this profile is a crap. Its not a heavy duty profile, just look at the design of it, with these holes and how the ribs are situated inside of it.

Of course depends how strong your machine you want to be.

Simply put: the ideal gantry alu profile is not born yet.

IMHO there are nice alu profile designs in the forums and the good ones have steel reinforcing plate on the gantry, one way or another.

The best so far alu implementation in a gantry i have seen is what Dean/JAZZCNC/ builds, so if you are for tidiness look there. And is not a profile.

This is the american way-bolting together profiles and having fear from some soldering. Shiny expensive useless machines. I was also a bit infected, thanks Dean that he cured me from the rack and pinion desire.

steel profile+square supported rails+ball screws=good machine worth spending some money for the build.

[routercnc]

Hi Andy,

In terms of how this section compares to others, I can only give you half the answer. The data they provide in the brochures is to allow you to then calculate bending deflection (from Ixx and Iyy) and bending stress (from Wxx and Wyy) depending on how you are going to load it. The G value is the modulus of shear (turning it into a parallelogram) which I don't think you can do much with for a gantry application.

They do not give you the twisting constant (which would allow you to calculate the amount of twist when you subject it to an offset load) because it would not give you an accurate answer as the profile is too complicated. There are values for simple shapes but all the others need FEA software.

The most useful thing for you is the Ixx and Iyy values. So to compare the performance I've shown the best calcs I can give you for 3 scenarios, one of which is your profile.

CONSTANTS (same for all cases):
Gantry length = 1m, Material = Aluminium, Cutting = Wood, Distance from cutting tool to centre of gantry = 150mm, Weight of Z axis 25kg

SECTION1 - RHS:
Width 80mm
Depth 160mm
Wall 6mm
Ixx 893cm4
Iyy 294mm4
X Deflection due to bending and twisting = 0.00117mm
Z Deflection due to sag from Z axis 0.007mm

SECTION2- Your Profile
Width 80mm
Depth 160mm
Ixx 944cm4
Iyy 183 cm4

I can't do further calcs on complex structure, but you can see that vertical bending will be no problem for 1 vs 2 (944cm4 vs 893cm4, but the horizontal bend and the twist (which is a much bigger factor) will be much worse for 2 (183cm4 vs 294cm4).

The best I can do is approximate your profile:
SECTION3 - Close approximation to your structure using I beam to achieve matching Ixx and Iyy
Width 120mm
Depth 160mm
Web 5mm
Flange 6mm
Ixx 989cm4 [ achieves similar to profile ]
Iyy 172cm4 [ achieves similar to profile ]
X Deflection due to bending and twisting = 0.041mm
Z Deflection due to sag = 0.006mm

Therefore you can see that in Z bending (due to weight of Z axis) it is very good and comparable to the RHS section (0.006mm vs 0.007mm).
But in X bending and twisting it is 35 times worse than the RHS (0.041mm vs 0.00117mm).

You might think that 0.041mm is OK for wood cutting, but remember that this is JUST the profile under ideal load transfer conditions (uniform distributed load) between all the bits attached to it. You will struggle to achieve UDL unless you apply very thick plates along the whole length, and then you are moving away from the simplicity. You also have to add all the other small deflections, plus the part that is impossible to calculate (for the DIY builder anyway) which is the effect of resonance effecting the finish.

If you ever want to cut Aluminium then the loads are about x10 compared to wood so your deflections will also be about x10. Thats 0.4mm in the X direction which is not really acceptable.

Hope this helps from a numbers point of view which is basically what you wanted to know.

From a recommendation point of view I would agree with the other posters.