SO3 Gantry Stiffness in Y direction

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wunderaa
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SO3 Gantry Stiffness in Y direction

Post by wunderaa » Mon Sep 14, 2015 9:01 pm

So I'm relatively new to CNC and have been poring over available information relating to the SO3 and many other platforms. I've put my unit through its paces with wood inlays, brass engraving and some aluminum milling. With all I've learned and experienced over the past couple of months, I've now come to what I feel is a shortcoming in the SO3 design: the stiffness of the gantry in the Y direction. Because the X axis is mounted to the front rail only (as opposed to straddling both sides like most machines) and because there is some play in the Z plate, this all adds up to Y directional flex. When I look at system limitations, feed rate seems to out rank all others because parts seem to start getting distorted. There was all this talk about how stiff the rails are (agreed!) but the gantry seems floppy in comparison.

Okay, so some numbers. I set up a 1/4" end mill in the collet and turned the unit on to hold everything in place. About 1" down on the end mill, I set up my dial indicator so I could measure deflection. Using one of those old spring-luggage scales, I applied about 2 lbs of force (or close enough...it's not really precise) in the 4 lateral directions of the bit. Results show below. Again, not terribly precise, but I'm building a case. And no, I didn't take a picture of the setup, as it was just for my curiosity at the time.

Negative Y - 0.114"
Positive Y - 0.111"
Negative X - 0.028
Positive X - 0.022

So, to the point. I was thinking of ways to stiffen up the gantry. I thought about mounting maker side along the back of the X axis, creating a rear plate with wheels that would connect to the main gantry, similar to how the XCarve is set up. Then would have to relocate electronics. Then there is the Z slide which seems to flex because of the v-wheels that are used. Not sure what could be done there except trying other wheels.

Anyone else think through this as they have gotten to know their SO3?

Fablicator
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Re: SO3 Gantry Stiffness in Y direction

Post by Fablicator » Mon Sep 14, 2015 9:34 pm

I think the plate the router is mounted to is the major issue, since the router aluminum mount is cantilevered so far away from the V wheels. I'd like to try a .625" thick aluminum replacement but I'm not sure how to make the offset nuts work well with a thick plate.

LTEPM
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Re: SO3 Gantry Stiffness in Y direction

Post by LTEPM » Mon Sep 14, 2015 10:02 pm

I added aluminum T-track to outboard edges of the Z-Carriage Plate which significantly reduced the amount of flex on my router bit.

I was also trying to determine how to make a new plate, but without the drawings, the T-Track was my quick and easy fix. Less than $20 and took about 2 hours total.

wunderaa
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Re: SO3 Gantry Stiffness in Y direction

Post by wunderaa » Mon Sep 14, 2015 10:59 pm

LTEPM wrote:I added aluminum T-track to outboard edges of the Z-Carriage Plate which significantly reduced the amount of flex on my router bit.

I was also trying to determine how to make a new plate, but without the drawings, the T-Track was my quick and easy fix. Less than $20 and took about 2 hours total.
Interesting. Pictures to share?

LTEPM
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Re: SO3 Gantry Stiffness in Y direction

Post by LTEPM » Tue Sep 15, 2015 4:28 am

Below are some photos of the T-Track used to stiffen the Z-Axis. I used Woodcraft T track and 1/8" x 3/4" aluminum bar to shim it for the 8-32 x 3/8" FHSS Screws. I drilled and tapped the Z carriage plate in 4 places on each side. This has reduced the flex in the Z axis plate significantly, still a little movement from the V-wheels. When the CAD files get posted for the users, I will make a new X carriage and Z carriage.
top view.jpg
Top View
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Attachments
side view.jpg
Side View
side view.jpg (40.92 KiB) Viewed 1865 times

AnonymousPerson
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Re: SO3 Gantry Stiffness in Y direction

Post by AnonymousPerson » Tue Sep 15, 2015 9:37 am

LTEPM wrote:When the CAD files get posted for the users, I will make a new X carriage and Z carriage.
Does this help?

http://www.shapeoko.com/forum/viewtopic ... =10#p53568
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WillAdams
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Re: SO3 Gantry Stiffness in Y direction

Post by WillAdams » Tue Sep 15, 2015 10:59 am

Interesting.

Edward posted a photo which included a U-shaped Z-axis spindle carriage plate — good endorsement of that.
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets
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AnonymousPerson
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Re: SO3 Gantry Stiffness in Y direction

Post by AnonymousPerson » Tue Sep 15, 2015 11:22 am

WillAdams wrote:Edward posted a photo which included a U-shaped Z-axis spindle carriage plate — good endorsement of that.
Do you have the link handy? :)
Shapeoko 3 #516

LTEPM
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Re: SO3 Gantry Stiffness in Y direction

Post by LTEPM » Tue Sep 15, 2015 12:25 pm

AnonymousPerson wrote:
LTEPM wrote:When the CAD files get posted for the users, I will make a new X carriage and Z carriage.
Does this help?

http://www.shapeoko.com/forum/viewtopic ... =10#p53568
It definitely helps for the Z axis, what I have in mind for the upgrade also requires a new X axis carriage.

WillAdams
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Re: SO3 Gantry Stiffness in Y direction

Post by WillAdams » Tue Sep 15, 2015 1:09 pm

I knew I was going to regret not making a note of that.

Here:

http://www.shapeoko.com/forum/viewtopic ... =20#p51901

(also adding it to the wiki...)
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets
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