Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: kolias on November 03, 2015, 09:38:07 AM

Title: Fixed Gantry Table
Post by: kolias on November 03, 2015, 09:38:07 AM

On a fixed gantry CNC I noticed some fix the gantry to the end of the base and some they have it in the center of the base.

Perhaps there is a reason but to my opinion having the gantry fixed to the center of the base should be the best option since the table will not travel as much

Which location is the best?

Title: Re: Fixed Gantry Table
Post by: BR549 on November 03, 2015, 01:19:49 PM

The gantry HAS to be mounted at the center of the table travel no matter how you do it.

Just a thought, (;-) TP

Title: Re: Fixed Gantry Table
Post by: Overloaded on November 03, 2015, 02:06:36 PM

On many, the gantry (Bridge) is substantially offset from center to ensure that the actual center-line of the tool is at the center of the table travel.
Depending on the design of the Z axis mechanisms, this offset can vary greatly.
Also, the arrangement of the linear components of the axis on the face of the gantry (Y or X) can, and usually does increase the the offset.

I think a "Gantry" type is where the gantry moves and a "Bridge" type is where the so called gantry (Bridge) is stationary.
Russ

Title: Re: Fixed Gantry Table
Post by: Overloaded on November 03, 2015, 02:16:50 PM

Here is a good example.
By the time the two axis' are mounted up, the tool will be well towards the center of the table travel range. By the apparent quality of this build, I's say "Spot on".
(all credit to the builder) :)

IIRC, Tweakie CNC is very similar.  :)
Russ  :)

Title: Re: Fixed Gantry Table
Post by: kolias on November 03, 2015, 02:58:42 PM

Kind of confusing for me..

BR549 says the gantry HAS to be mounted at the center of the travel and
Russ says the gantry is substantially offset from the center which I don’t understand why

I will wait to see if others have a different opinion

Title: Re: Fixed Gantry Table
Post by: Overloaded on November 03, 2015, 03:18:06 PM

Terry is right ... he's ALWAYS right.  :)   ;D

But I'm fairly certain that he is referring to mounting the bridge WHEREVER NECESSARY to position the center-line of the Z axis directly over the midpoint of the table travel.

I've illustrated as best as I can.

Think about it.

 :)

Title: Re: Fixed Gantry Table
Post by: kolias on November 03, 2015, 03:27:07 PM

Sorry Russ, not clear to me

But reading again Terry and you I think you say the same thing but in different ways, that is the gantry must be mounted at the center of the table travel.

Title: Re: Fixed Gantry Table
Post by: Overloaded on November 03, 2015, 03:38:29 PM

Here is one more example.
I hope it helps,
Russ :)

Title: Re: Fixed Gantry Table
Post by: kolias on November 03, 2015, 04:13:33 PM

Thanks Russ for your time, now I got it

Much appreciated

Title: Re: Fixed Gantry Table
Post by: BR549 on November 03, 2015, 04:28:21 PM

Russ explained it properly (;-)

I would not offset the spindle any more than neccesary. I would center mount it IF possible so there would be Zero offset forces involved. But that is just me. Your mileage may vary.
(;-) TP

Title: Re: Fixed Gantry Table
Post by: garyhlucas on November 03, 2015, 06:20:50 PM

I hate moving tables. They always spill my coffee during rapids.

Title: Re: Fixed Gantry Table
Post by: BR549 on November 03, 2015, 06:39:05 PM

That is why they make Scurve trajectories no spilled coffee.

(;-) TP