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Axel1966 Sat 03 March 2012 04:48

@ Ken
Thanks for this precisions. Sorry, you post faster than I can reply :)

The larger gantry beams may induce a modification of the 10.20.451-452 parts, right ?
Those are lasercut parts, a very sensible subject in the MM building through.

When I talk about precision, I don't know exactly.
0,1mm will be pretty enough.
The most important is to get an accurate cut, especialy on curves.
The edges must be without defauts.
If the MM shape is good, I guess, it might be a question of motor reduction, rigidity and vibrations...

Axel1966 Sat 03 March 2012 14:58

For example, I would avoid this :

KenC Sat 03 March 2012 22:21

In my humble opinion, 0.5mm is already "too accurate". In some occasions when I made an mistake or error in dimensions, even 3mm error is not visible.

with a taller gantry beam, youneed to modify 10.20.451~2 and also 10.20.456

The common solution to the chatters at curve are solved in 2 way,
1) Belt-reduction
2) Sand paper :D

Axel1966 Sun 04 March 2012 02:30

Yep, sanding means also errors, especialy on curves, but it's unavoidable, anyway.
I guess I must also be very acurate on the build to minimize cuting defaults.
I'm realy affraid about any modification of the laser parts. :(
Any error conducts to problems and/or leads to new expensive laser parts.
As you said, I'm not brave enough ! :D

In this post : What is the max Gantry width allowable ?
Gerald says that he don't see big problems about 96" (3m) Y gantry.
Mine should be less than 3 meters (2940, to be confirmed by official plans, plans I must buy next month...).
For a 3,5m gantry, he says the static flex of a 4mm thick 3.5m tube is less than the static flex of a 2mm thick 2m tube, but he was thinking about low frequencies vibrations.

According my MM must have a belt reduction (to be calculated later), what about filling the Y beams to reduce vibrations ?
Does it have been tested yet ?
Polyurethane foam may limit the resonance but won't add significant weight.
Filling beams with concrete will, and reduce considerabily vibrations,
through, even with light weight concrete (styrofoam and nylon fiber charged) the weight can be too much important for motors and other parts.
The gantry manipulation will need at last 4 people ! :D

Well I don't know if it's a real good idea.
I would rather using the right shape with the right thickness...

KenC Sun 04 March 2012 03:17

Well... you can always build one & experiment with the filling. No one know to what degree vibration will start to affect your cut results... so it is really a shot in the dark.

remember to factor in the weight of the filling. never know if it will increase static deflection.

My philosophy... If you are not brave enough to modify the laser files, you should not waste time in customising your own & stick to the "standard" design, or build a smaller machine. or get a bigger work shop to house your machine.

Axel1966 Sun 04 March 2012 05:06

I respect your philosophy, Ken.
I would love to have a huge workshop, it's still a goal...
Maybe in the future if the MM project is successfull and brings money back.

Modifying the laser parts path is not impossible. Technicaly, it's even easy.
But any change at this point might induce stunt changes.
I'll do it as a last resort.

I would like to make this project possible with the specifications I have to deal with.
I've read a lot the MM forum. My MM won't be se single that can be dismountable.
I've read also that large Y beams are possible.

I worked a lot on the table at this point.
I have by my side a cutting list optimised for 6000mm steel bars.
Except for the Y beam vibration factor which must be still discussed,
it seems to me as strong as possible compared to the standard design.
Profiles matches at last standard specifications and this is triangulation on each sides.
I wish I did not make too much mistakes on it...
I do not have the approval of the MM community yet.

For the gantry, let's follow Gerald advice and plan on 100x50x4mm beams.
If this profile's ok, I can test the filling method for the community, if it's not stupid.
What is the max weight the motors/rail/rollers can stand ?

Axel1966 Sun 04 March 2012 14:20

uh... Anyone ? :o

smreish Mon 05 March 2012 06:55

BWC #3 Vee wheels are rated each at:
382 # Axial
1326# Radial
for loading

The bigger issue is Torque with relation to drawbar required to accelerate, maintain and decelerate with respect to the mass.

I know from experience, that a 77" long gantry from 4 x 2 x 1/4" Steel Mechanical Tube is just fine with 7.2 OM motors. Average top speed of 325ipm, nominal 180-225ipm for most work. This is with a 40# extended Z-slide in place and spindle. SO, my machine "load package" in the y-car is about 60# heavier than all the rest.

Does this help?


bozona1 Mon 05 March 2012 09:44


Would you be able to load material over the rails, with your gantry parked at the end of your x? That way you would have a significantly less massive gantry?:rolleyes:
Just a thought...

Axel1966 Mon 05 March 2012 10:48

Hi all, thanks a lot for your help.

Don, I thought about that, this could solve a lot of problems,
but the overall access to clamp parts and boards would be quickly unbearable...

Sean, thanks for the link and data. It seems the rollers can stand much more than they do usualy. But not the stepper motors.
you must have a very heavy gantry. I guess the cut is nice with this weight.
With 1/4" thick, your two 77" beams have a total weight of 106 pounds (1/4" = 6mm).
My Y beams must be a bit less than 116" long.
To stay in a close weight than yours, I should go to a 5/32" (4mm) thick tube.
It's the specifications Gerald gave in the topic about long gantrys.
So filling the tubes with concrete, is a bad idea because the motors will not stand that extra weight.
Even 5 or 6mm (16/64" or 1/4") thick tubes must be too heavy.
62kg (135 pounds) for the 5mm and 72kg (160 pounds) for the 6mm. Hum.
I wanted to order those. Hopefully, you warned me before.

Do you have a belt reduction Sean ?
Do you think a belt reduction can compensate an extra gantry weight ?

A new question for all, did you bought hot or cold rolled steel for your MM parts ?
I quess the best is hot-rolled steel but is the difference important for the MM ?

smreish Mon 05 March 2012 12:29

As I mentioned before, I am using the 7.2:1 Gearbox motors from Oriental Motors with 20T pinions. The highest reduction possible for the best resolution possible with most considered.

I am not a speed demon, but the machine performed well with this mass. I never pushed the machine beyond 350 on quick moves because of the added mass.

Axel1966 Tue 06 March 2012 14:35

Thanks Sean, I did not get 7.2 was for the reduction, not for amperage.
Sorry, newbie inside.

Some people says "long" motors have more torque, is it right ?
At this point, I don't understand a lot about the steppers, are your "short" OM PK296A2A among the most powefull nema34 ?
Could other steppers be even better for heavy gantries ?
Otherhand, Gerald said that too big motors are not adapted to the MM...

Othewise, I searched on the forum and did not found if steel must be hot rolled or not...
I'll take Hot rolled steel anyway, it's more expensive but I guess it's better.

Axel1966 Mon 12 March 2012 08:24

Hi all,
I've modified the table base according to comments above.
Can you tell me what's wrong or if it looks ok for your wise eyes ?
Thanks. ;)

Here's the rough :
Front view :
Right view :

danilom Mon 12 March 2012 08:48

You solved nothing about racking when using indexer with that cross bearer. it should go straight to the ground to stabilize it.

Axel1966 Mon 12 March 2012 09:42

Thank you for your message Danilo,
I get what you mean.

While 4th axis is not implemented, the Gantry will not have to go so far.
I'll fix the proximity sensors and the stopper near 1220mm for now.
I thought those cross bearers beeing here temporary.
And I had 1300mm left on my ⌀40 6m tube.
They might be of no use for now and for later... :o Hum, I'm sorry about that...
Maybe a plan will explain better than a simple view :

KenC Mon 12 March 2012 22:54

I don't think using C-channel for the cross beam which support the cross-bearer is a good idea. I will strongly recommend 200x50x3mm RHS for the job.
Also, it will be better if you place the cross bearer on top of this 200x50x3mm RHS, it will be structurally more efficient & a lot easier to fabricate.
I sense that you want are building your machine for mainly storage cabinet because you removed all the critical supporting trusses from the table... You gotta make up you mind whether you want your table structure to be a storage cabinet or to support your MM mechanism. My philosophy says a multiple purpose equipment will never perform a single task perfectly because of all the compromises you design into it. Like all thing in life, you can't have it all...

Axel1966 Tue 13 March 2012 03:20

Well your comment is full of sense ! Thank you.

I thougth storage in the table will add mass which may stabilise the basis.
But if there's some structural problems, I should reconsider.
To strenght the long table beam, I thought about a cable straightener (like in architecture), but I left it because it's not cheap and complicated to build.
The stock may be simply under the table, on a simple frame.

Aren't the 70x40mm UPN chanels in Gerald's original maps ? (I did not bought them yet, next month, I promiss :o)
Well with 8mm thick, UPN seems to me easy to tap and bolt.
Maybe It's possible to bolt the 200x50x3mm RHS, passing through them with long bolts.
I'll try to find if I can find some, and ask about their price.

Thank you for your help.

Gerald D Tue 13 March 2012 04:15

Axel, I am not going to spend time analysing your design in detail, but I can "feel" that it is quite weak. I estimate that if I sit on the front edge of your design, it will go down at least 2mm, maybe 5mm.

You can use your design, but you will have to reduce the cutting speeds to stop the system from vibrating/resonating and giving you a poor cut quality.

KenC Tue 13 March 2012 04:31

Axel, 3m is a long span any sort of structure beam...RHS will be lighter & more rigid. With this sort of extended span, I usually reduce the beam weight as far as I could to reduce sagging due to its own weight. You can add weight else where if you wish.
Cable suspension won't really help here as you load will be moving along the beam & the cable suspension will deform the beam differently when the car moves.
IF you wish to enjoy the easy work on UPN & have plenty of weight; Brude force method is use the same UPN which you use for your rail support to support your cross bearer. I can be very sure that will work.

Axel1966 Tue 13 March 2012 04:34

I understand Gerald.
Thank you for your regard, the time spent, and your advice,
I must reconsider anyway. The table storage is a real bad idea.
And last, it's more expensive. Let's do simple and efficient.

Axel1966 Tue 13 March 2012 05:28

Ok thank you ken, I'll take your advice under consideration.

Metalsmith Wed 04 April 2012 17:38

I can send you a link to a app that will print out wrap-a-rounds for round is metric and you put in size of tube and angle anf it will print a pattern .... You want stiffness and light, think The Eiffle Tower ....trianglate, make girders !

Axel1966 Thu 05 April 2012 02:14

Well, I think actualy to oversize materials, but I love experiments,
I'm interested in your link. Thanks.

Metalsmith Thu 05 April 2012 08:41 tubemiter.exe ..... it's at the bottom of page, there are other apps that might be used

with this , a hacksaw and files, you can miter any tube !

Axel1966 Thu 05 April 2012 15:51

Thank you very much, I will check it out. :)

Axel1966 Thu 05 April 2012 16:04

Very useful for a dumb like me ! Thanks
A permalink for the soft from my server : Tubemiter.exe

Metalsmith Fri 06 April 2012 10:37

Before I build my tube bender......
I made motorcycle frames with a 1" electrical conduit bender ( Same as 1.25" crew tube), die grinder, hacksaw and the miter program.... ; )

KenC Fri 06 April 2012 20:48


Metalsmith Sat 07 April 2012 10:01

Originally Posted by KenC View Post

WTI Sat 07 April 2012 17:26

He is asking you if you TIG welded your motorcycle frames. You know; "stacking dimes".

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