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Author Topic: Gantry Slack  (Read 4210 times)

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Offline kolias

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Gantry Slack
« on: March 27, 2011, 01:23:15 PM »
So far the CNC is performing very well and all patterns I have cut on MDF (straight lines, circles, curves) are perfect.

However I have noticed a slight left/right play on the gantry. When I hold the router bit and try to see if there is any slack the gantry moves in the X direction perhaps by 1/32”.

So I thought that it may be a good idea to install a 3/8” threaded rod as per attached picture. This rod will go through the gantry on both sides with a 1/8” aluminum plate on the inside and 1/8” aluminum angle (see picture) on the outside of each vertical piece of the gantry and nuts on both sides holding tight the components.

I’m planning to first home the Y axis so I know that is square and then drill the holes to attach the pieces.

Do you think it is a good idea or not?
Nicolas

Offline kolias

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Re: Gantry Slack
« Reply #1 on: March 30, 2011, 06:18:51 PM »
Dont know why no one replied to this post; I was just looking for comments and not endorsement

Anyway I decided to install an aluminum angle 1"x 1"x 1/8" instead of the threaded rod as per attached pics.

Did not noticed any movement after the installation but have to do an actual cut to see the real results
Nicolas

Offline Hood

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Re: Gantry Slack
« Reply #2 on: March 30, 2011, 07:01:13 PM »
Glad to see you got the better of it. Was going to reply after I read it but was at work and had to do something else and just plain forgot :(
Hood

Offline kolias

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Re: Gantry Slack
« Reply #3 on: March 30, 2011, 07:59:47 PM »
I thought my idea was so crazy that nobody bothered to reply LOL

I’m happy you approve Hood
Nicolas

Offline Sage

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Re: Gantry Slack
« Reply #4 on: March 30, 2011, 08:57:02 PM »
I'm assuming your problem was that the gantry was able to lean side to side.

Making an X with two angle irons rather than one like you have would probably be better but:

I'm wondering if a flat rectangular MDF board across where you have the angle iron with several screws (and maybe some glue) on each end might make it more rigid. (below the shelf and angled edge and as low as you can go). That would box it in and make it very rigid. (IMHO). (Heavier though).

Sage
« Last Edit: March 30, 2011, 09:02:58 PM by Sage »

Offline ger21

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Re: Gantry Slack
« Reply #5 on: March 30, 2011, 09:37:15 PM »
That single layer of MDF for the sides is always going to be a weak point. What I've seen done on simialar machines is use some heavy steel angle down the sides, to reduce the flexing.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline kolias

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Re: Gantry Slack
« Reply #6 on: March 31, 2011, 12:02:46 AM »
You are right Sage, leans side to side by about 1/32”. As you can see from the attached pic. your idea was my 1st try but for some reason didn’t work well and I had to remove it. Adding one more angle to make an X with two angles is my next step if I see no improvement but so far she feels solid.

Gerry the sides of the gantry are not MDF but rather 3/4" plywood. I don’t know which one is more resistant to bending but thought that plywood would be better. You idea about the steel angles down the side was one of my 1st thoughts but after careful observation I noticed that its not the sides that are bending but rather the whole gantry assembly leans from side to side and therefore an X bracing looks like to be the answer.

As I mentioned, the machine works very well and the only problem so far is when I cut circles less then 1.5” diameter the circles are not perfect circles. Cutting larger circles, curves and lines there is no problem

Thank you both for your help
Nicolas

Offline ger21

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Re: Gantry Slack
« Reply #7 on: March 31, 2011, 07:00:27 AM »
With smaller circles, try cutting them slower. It's probably caused by flexing due to the rapid direction changes.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline Sage

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Re: Gantry Slack
« Reply #8 on: March 31, 2011, 08:21:31 AM »
Provided you had screws into that piece of plywood from the sides as well, I would have thought that should take care of your problem. Surprising.  :-\

Whatever works I guess.

Sage

Offline kolias

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Re: Gantry Slack
« Reply #9 on: March 31, 2011, 08:45:47 AM »
Good idea Gerry, I will give it a try

Sage, yes I had three #8 x 3” long screws on each side but no glue. Perhaps the glue might have done the trick but now I like better the aluminum angle

Nicolas