Re: [Emc-users] Beam Stiffening?

[Chris Albertson]

I think I fell for the “beam is bending” idea too.   It might be.   The way to 
find out is to measure the beam center with the dial indicator and then measure 
the ends of the beam.   It might be that the entire beam is moving

Is the gantry belt driven?   Long belts can act like springs.  The solution is 
wider belts.  It is easy to see that a belt that is twice as wide is twice as 
stiff.

I’d measure movement at the ends before any more thinking about the beam.

As for modifying the beam, you have to model it.  Guessing and “eyeball 
engineering” generally does not work well.   Any fix is going to be very 
expensive.  It is best to know it will work.


Everything that you add to that beam also adds mass.   Mass is what you want to 
get rid of.





> On May 14, 2024, at 1:56 PM, gene heskett  wrote:
> 
> On 5/14/24 14:34, Eric Keller wrote:
>> Do something cheap because I'm not convinced it's the beam.  I've done
>> troubleshooting on things like this, and sometimes it's stiffness and
>> sometimes it's not stiffness. But it really doesn't make sense that it
>> would sit there and ring after a move, so you also may have some
>> tuning to do.  Possibly a notch filter?
>> Eric Keller
>> Boalsburg, Pennsylvania
>> On Mon, May 13, 2024 at 4:50 PM Todd Zuercher via Emc-users
>>  wrote:
>>> 
>>> Anyone have any brilliant ideas to stiffen a woefully inadequate cross beam 
>>> on a gantry router without adding too much mass?  What is there now is a 4" 
>>> x 8" rectangular 3/8" walled extrusion that is 145" long.
>>> 
>>> Under normal jogging commands the two servos control the ends of this 
>>> gantry reasonably well, but while the axis is homing the thing shakes and 
>>> wobbles terribly bad.
> 
> This, on 3rd or 4th read, sounds as if the two servo's are not in tune with 
> each other.  Tuning servo's is not my strong suit, (and the only servo I had 
> was destroyed by the new autotune pid in linuxcnc, it found settings that mde 
> it ocillate and fried a $125 motor in around a minute. But this would be a 
> lot easier to synchronize if stepper/servo's were used. Rigged with a home 
> switch, maybe a prox switch since its non contact, with logic rigged so they 
> can back away from home and move in sync the rest of the day, getting sync is 
> running toward home until the switch trips on that end of the beam, run 
> toward home until both ends have tripped, call that home. From then until 
> powerdown, both motors getting the same step/dir signals will be in sync till 
> the powerdown. No fighting because the two servo's are not in an identical 
> state of tune. Hanpose has nema 34 and 42 motors of 12 NM, probably with more 
> torque and speeds than your servo's. The best description is that they just 
> work. And they use much less power than regular steppers to get the job done. 
> A diff you can see in the power bill if replacing burn your hand regular 
> steppers.
> 
> How fast and how strong are the servo's you are using now? Gear ratio's too.
> 
>  Also If I put a dial indicator in the center of the bridge and hit the 
> bridge forward or backward it will flex and wobble enough to displace the 
> dial indicator +/-0.03 and it takes nearly a dozen wobbles to dampen it.  But 
> on the ends the servo's only have a few thousandths of give.
>>> 
>>> I'm less concerned about the actual stiffness and more worried about 
>>> dampening the wobble.
>>> 
>>> Todd Zuercher
>>> P. Graham Dunn Inc.
>>> 630 Henry Street
>>> Dalton, Ohio 44618
>>> Phone:  (330)828-2105ext. 2031
>>> 
>>> 
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> 
> Cheers, Gene Heskett, CET.
> -- 
> "There are four boxes to be used in defense of liberty:
> soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author, 1940)
> If we desire respect for the law, we must first make the law respectable.
> - Louis D. Brandeis
> 
> 
> 
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Re: [Emc-users] Beam Stiffening?

[gene heskett]

On 5/14/24 14:34, Eric Keller wrote:

Do something cheap because I'm not convinced it's the beam.  I've done
troubleshooting on things like this, and sometimes it's stiffness and
sometimes it's not stiffness. But it really doesn't make sense that it
would sit there and ring after a move, so you also may have some
tuning to do.  Possibly a notch filter?
Eric Keller
Boalsburg, Pennsylvania

On Mon, May 13, 2024 at 4:50 PM Todd Zuercher via Emc-users
 wrote:


Anyone have any brilliant ideas to stiffen a woefully inadequate cross beam on a gantry router 
without adding too much mass?  What is there now is a 4" x 8" rectangular 3/8" 
walled extrusion that is 145" long.

Under normal jogging commands the two servos control the ends of this gantry 
reasonably well, but while the axis is homing the thing shakes and wobbles 
terribly bad.


This, on 3rd or 4th read, sounds as if the two servo's are not in tune 
with each other.  Tuning servo's is not my strong suit, (and the only 
servo I had was destroyed by the new autotune pid in linuxcnc, it 
found settings that mde it ocillate and fried a $125 motor in around a 
minute. But this would be a lot easier to synchronize if stepper/servo's 
were used. Rigged with a home switch, maybe a prox switch since its non 
contact, with logic rigged so they can back away from home and move in 
sync the rest of the day, getting sync is running toward home until the 
switch trips on that end of the beam, run toward home until both ends 
have tripped, call that home. From then until powerdown, both motors 
getting the same step/dir signals will be in sync till the powerdown. No 
fighting because the two servo's are not in an identical state of tune. 
Hanpose has nema 34 and 42 motors of 12 NM, probably with more torque 
and speeds than your servo's. The best description is that they just 
work. And they use much less power than regular steppers to get the job 
done. A diff you can see in the power bill if replacing burn your hand 
regular steppers.


How fast and how strong are the servo's you are using now? Gear ratio's too.

  Also If I put a dial indicator in the center of the bridge and hit 
the bridge forward or backward it will flex and wobble enough to 
displace the dial indicator +/-0.03 and it takes nearly a dozen wobbles 
to dampen it.  But on the ends the servo's only have a few thousandths 
of give.


I'm less concerned about the actual stiffness and more worried about dampening 
the wobble.

Todd Zuercher
P. Graham Dunn Inc.
630 Henry Street
Dalton, Ohio 44618
Phone:  (330)828-2105ext. 2031


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Cheers, Gene Heskett, CET.
--
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis



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Re: [Emc-users] Beam Stiffening?

[Dave Engvall]

This is why I’m a chemist not an engineer. So how does it break out cost vs 
results, not exactly the same as weight. Even tho it is not an aircraft app 
working towards lightness may make sense. Thanks for the elucidation. Really 
happy it is not my problem. ;-)  A Boeing engineer once commented that 
non-aeronautical applications were SO easy to make strong/stiff!

> On May 13, 2024, at 4:02 PM, andy pugh  wrote:
> 
> On Mon, 13 May 2024 at 22:50, Chris Albertson 
> wrote:
> 
>> Adding anything inside is the worst place to add material.
> 
> 
> Yes, without a doubt, but it seems fair to assume that the ganry has slides
> and other components on the outside, but not on the inside.
> 
> The base beam has an Iyy (bending in the plane of the smaller dimension )
> of 22in^4
> Doubling it internally gives: 34.2in^4, so about 50% stiffer
> Doubling externally gives: 57in^4 so getting on for 3x as stiff.
> 
> I admit I was imagining a thinner wall thickness relative to the overall
> dimensions, where the difference would be smaller.
> 
> There is less to be gained than you might think from making the section
> solid. You can do the experiments here:
> https://amesweb.info/section/second-moment-of-area-calculator.aspx
> 
> If stiffness is the key, then add a stiff material.
> Aluminium is 68GPa (moving away from measuring in bananas)
> Steel is 200GPa (this is the same for all iron alloys, hardened or
> unhardened, including cast iron)
> Titanium is 114GPa, so good for light, not for stiff.
> Carbon fibre is 181Gpa for uindirectional fibres, but more typically around
> 50GPa.
> Tungsten carbide is 600GPa (which is why solid carbide boring bars exist)
> Beryllium is 287 but probably out of both budget and COSHH limits.
> 
> -- 
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is designed
> for the especial use of mechanical geniuses, daredevils and lunatics."
> — George Fitch, Atlanta Constitution Newspaper, 1912
> 
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Re: [Emc-users] Beam Stiffening?

[Eric Keller]

Do something cheap because I'm not convinced it's the beam.  I've done
troubleshooting on things like this, and sometimes it's stiffness and
sometimes it's not stiffness. But it really doesn't make sense that it
would sit there and ring after a move, so you also may have some
tuning to do.  Possibly a notch filter?
Eric Keller
Boalsburg, Pennsylvania

On Mon, May 13, 2024 at 4:50 PM Todd Zuercher via Emc-users
 wrote:
>
> Anyone have any brilliant ideas to stiffen a woefully inadequate cross beam 
> on a gantry router without adding too much mass?  What is there now is a 4" x 
> 8" rectangular 3/8" walled extrusion that is 145" long.
>
> Under normal jogging commands the two servos control the ends of this gantry 
> reasonably well, but while the axis is homing the thing shakes and wobbles 
> terribly bad.  Also If I put a dial indicator in the center of the bridge and 
> hit the bridge forward or backward it will flex and wobble enough to displace 
> the dial indicator +/-0.03 and it takes nearly a dozen wobbles to dampen it.  
> But on the ends the servo's only have a few thousandths of give.
>
> I'm less concerned about the actual stiffness and more worried about 
> dampening the wobble.
>
> Todd Zuercher
> P. Graham Dunn Inc.
> 630 Henry Street
> Dalton, Ohio 44618
> Phone:  (330)828-2105ext. 2031
>
>
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Re: [Emc-users] Beam Stiffening?

[Dave Engvall]

Hi all, 
Since I’m cheap I’d prototype with a fiberglass tube and fill with urethane 
foam. How much does the modulus change between a rectangular tube and 
elliptical geometry?
Box with corner braces that are viscous damped. It all comes down to load and 
frequencies. 
I’m just the aging dummy in the corner. ;-)

> On May 13, 2024, at 2:36 PM, Chris Albertson  
> wrote:
> 
> 
> 
>> On May 13, 2024, at 1:45 PM, Todd Zuercher via Emc-users 
>> mailto:emc-users@lists.sourceforge.net>> 
>> wrote:
>> 
>> Anyone have any brilliant ideas to stiffen a woefully inadequate cross beam 
>> on a gantry router without adding too much mass?  What is there now is a 4" 
>> x 8" rectangular 3/8" walled extrusion that is 145" long.
>> 
>> Under normal jogging commands the two servos control the ends of this gantry 
>> reasonably well, but while the axis is homing the thing shakes and wobbles 
>> terribly bad.  Also If I put a dial indicator in the center of the bridge 
>> and hit the bridge forward or backward it will flex and wobble enough to 
>> displace the dial indicator +/-0.03 and it takes nearly a dozen wobbles to 
>> dampen it.  But on the ends the servo's only have a few thousandths of give.
>> 
>> I'm less concerned about the actual stiffness and more worried about 
>> dampening the wobble.
> 
> 
> What is the extrusion made of, I assume it is some kind of aluminum alloy.
> The simplest but expensive option is to replace it with a stronger/stiffer 
> material with the same dimensions.   Of course Titanium comes to mind but 
> that is maybe not in the budget.Carbon fiber could work and it is 
> possible to DIY carbon fiber beams with just hand tools.   I have made 4 
> meter long racing kayaks with carbon, using just a paint brush and scissors 
> in one weekend.   
> 
> The first class way is to make a female mold and polish it well so the part 
> looks nice.   The cheap way is to make one like they make surfboards.  You 
> start with a foam block, shape it then wrap it in fiber and resin.
> 
> The neat thing about carbon composite is that you are not limited to the 
> extrusion shape.   I would make the entire beam a compound curve with no flat 
> or straight or cylindrical sections,  Maybe like a very elongated American 
> football but with ovil cross section.
> 
> I like to use the car hood story.  A flat sheet of sheet steel is bendable by 
> hand.  But after they stamp it into the shape of a car hood it becomes rigid. 
>   So rather then a square tube, way not oval but with a larger diameter in 
> the center where all the bending force is?
> 
> The way you make it is to first make a full-size model out of wood and bondo. 
> Do a test-fit and give it an automotice grade paint finsh and then paste wax. 
>  Make a fiber glass mold, then from that your part.   Yes that is a lot of 
> work.  This is why you have an aluminum extrusion there now, because that was 
> easy and cheap.
> 
> 
> 
> 
> 
> 
>> 
>> Todd Zuercher
>> P. Graham Dunn Inc.
>> 630 Henry Street
>> Dalton, Ohio 44618
>> Phone:  (330)828-2105ext. 2031
>> 
>> 
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> 
> 
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Re: [Emc-users] Beam Stiffening?

[Chris Albertson]

This kind of design “works” only if you make the overall dimension MUCH larger. 
   It is an overall more efficient design but bmovimng material does not add 
streght of stiffness.  You would need to do something like scale the beam up to 
maybe twice its size then cut away half the metal.

The first step should be to look for a material with the best stiffness to 
weight ratio you can afford.  Then if you change the shape, you woiuld have to 
go outside of the current 4x8 dimensions.

“Strength” is not just the tensile strength of the material but, that tiimes 
the cross sectional area,  and then you multiply by the distance from a kind of 
“center line”.   

The problem is cost.  The machine has the aluminum extrusion likely because it 
was the loest cost reasonable solution.   They could have used a high grade of 
tool steel machine into a truss frame but that might cost more than some cars.

My suggestion of carbon fiber has because the materials are not super expensive 
but what you pay for is the huge amount of labor

Whatever you do it will cost a bunch more then that extrusion.  So be sure to 
have it modeled using finite element analysis.  You hate to spend $10K or more 
only to find iot made thins worse.



> On May 14, 2024, at 3:21 AM, Gregg Eshelman via Emc-users 
>  wrote:
> 
> A triangular tube with an isogrid pattern cut into it to reduce mass without 
> sacrificing stiffness. Could have it laser cut with slots on the fold lines 
> to make it easy for a sheet metal break to fold accurately. The design could 
> have tabs and slots to interlock on the joining edge. Then TIG weld along the 
> bend slots and joining edge. Weld it like they do top fuel dragster frames, a 
> little bit here, a little bit there - to eliminate warping.
> 
> Or it could be possible to design three panels to bolt together and to the 
> gantry using tabs and Rivnuts.
> 
> The round holes at the vertexes of the triangles wouldn't need to be cut, 
> except in places where you'd want Rivnuts to mount things.
> 
> For isogrid design there's the 1973 book 
> https://femci.gsfc.nasa.gov/isogrid/index.html Page 42 of the PDF has the 
> dimensions for the panels used for walls and floors in Skylab. The photos in 
> it are mostly useless since the PDF was apparently produced from a microfiche 
> of a FAXed (or early non-greyscale photostat) copy of an original printed 
> copy of the book.
> 
> In some dusty, forgotten file cabinet there must be an original printed copy 
> of
> Isogrid Design Handbook - NASA CR-124075, Rev. A, Feb. 1973
> 
> A triangular tube is more twist and bend resistant than a square, 
> rectangular, or round tube, and it is lower mass than a square or rectangular 
> tube. Even less mass with all the bits removed to cut an isogrid.
> 
> On Monday, May 13, 2024 at 02:49:51 PM MDT, Todd Zuercher via Emc-users 
>  wrote: 
> 
> Anyone have any brilliant ideas to stiffen a woefully inadequate cross beam 
> on a gantry router without adding too much mass?  What is there now is a 4" x 
> 8" rectangular 3/8" walled extrusion that is 145" long.
> 
> Under normal jogging commands the two servos control the ends of this gantry 
> reasonably well, but while the axis is homing the thing shakes and wobbles 
> terribly bad.  Also If I put a dial indicator in the center of the bridge and 
> hit the bridge forward or backward it will flex and wobble enough to displace 
> the dial indicator +/-0.03 and it takes nearly a dozen wobbles to dampen it.  
> But on the ends the servo's only have a few thousandths of give.
> 
> I'm less concerned about the actual stiffness and more worried about 
> dampening the wobble.
> 
> 
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Re: [Emc-users] Beam Stiffening?

[Gregg Eshelman via Emc-users]

A triangular tube with an isogrid pattern cut into it to reduce mass without 
sacrificing stiffness. Could have it laser cut with slots on the fold lines to 
make it easy for a sheet metal break to fold accurately. The design could have 
tabs and slots to interlock on the joining edge. Then TIG weld along the bend 
slots and joining edge. Weld it like they do top fuel dragster frames, a little 
bit here, a little bit there - to eliminate warping.

Or it could be possible to design three panels to bolt together and to the 
gantry using tabs and Rivnuts.

The round holes at the vertexes of the triangles wouldn't need to be cut, 
except in places where you'd want Rivnuts to mount things.

For isogrid design there's the 1973 book 
https://femci.gsfc.nasa.gov/isogrid/index.html Page 42 of the PDF has the 
dimensions for the panels used for walls and floors in Skylab. The photos in it 
are mostly useless since the PDF was apparently produced from a microfiche of a 
FAXed (or early non-greyscale photostat) copy of an original printed copy of 
the book.

In some dusty, forgotten file cabinet there must be an original printed copy of
Isogrid Design Handbook - NASA CR-124075, Rev. A, Feb. 1973

A triangular tube is more twist and bend resistant than a square, rectangular, 
or round tube, and it is lower mass than a square or rectangular tube. Even 
less mass with all the bits removed to cut an isogrid.

On Monday, May 13, 2024 at 02:49:51 PM MDT, Todd Zuercher via Emc-users 
 wrote: 

Anyone have any brilliant ideas to stiffen a woefully inadequate cross beam on 
a gantry router without adding too much mass?  What is there now is a 4" x 8" 
rectangular 3/8" walled extrusion that is 145" long.

Under normal jogging commands the two servos control the ends of this gantry 
reasonably well, but while the axis is homing the thing shakes and wobbles 
terribly bad.  Also If I put a dial indicator in the center of the bridge and 
hit the bridge forward or backward it will flex and wobble enough to displace 
the dial indicator +/-0.03 and it takes nearly a dozen wobbles to dampen it.  
But on the ends the servo's only have a few thousandths of give.

I'm less concerned about the actual stiffness and more worried about dampening 
the wobble.


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