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Without a grand amount of additional structure to your gantry design... you will be disappointed with the machine's operation. There just is not sufficient material size, spacing, or bracketing with that design.
Senna
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My first extrusion cnc router. My pieces should be here Monday.
Without a grand amount of additional structure to your gantry design... you will be disappointed with the machine's operation. There just is not sufficient material size, spacing, or bracketing with that design.
Senna
aka BOOMER52 >>> http://www.rcgroups.com/forums/member.php?u=159693
I do have 1/4" bracketery plating going on either side of the gantry and on every joint and corner. I just didn't knkow how to draw them with that software
I'm truly not wanting to disparage something you have obviously spent some time at designing... it's just that the gantry design as pictured... even with the 1/4" attach plates at each upright interface uses insufficiently sized extrusions. It looks to be 1515 (if it's 8020 extrusions) or 1-1/2" sq. Unless you completely box the upper and lower gantry head span ties you will most certainly experience an unacceptable amount of deflection.
Maybe you have something in mind that you were also unable to draw that addresses this... but it will need to be robust. 3030 series or 3" sq extrusions would even be marginal without additional stiffening for your gantry span.
With the pieces on the way... this advice is a bit too late. I hope I'm making assumptions without having all the facts and it works out for you.
Senna
aka BOOMER52 >>> http://www.rcgroups.com/forums/member.php?u=159693
I'll post a few photos after I get it built...I will also check deflection with my dial indicator under different weights...for now thats the best I can do...
You will most likely also want to put an additional set of legs in the middle of the X-axis. That's also too long of a span to be unsupported if you are going to have any weight on the gantry or table.
Would 1/4" x 2" running the entire length bolted 4" oc on the outside workOriginally Posted by Bear5k
I assume you are thinking of doing a "buddy board" of some kind? What do your deflection calculations indicate is the deflection in the material in question by itself? How much will your gantry weigh when fully-loaded (Z-axis, router, motors, hoses, cables, etc.)? What level of accuracy are you looking to achieve?
There are four major sources of error that you need to control with your build:
1) Positioning Error - This is the error inherent in the linear axes. Get a decent screw, and this can be controlled relatively easily.
2) Deflection - This is the error from the frame bending. You have the weight of the various pieces combined with any cutting forces applied.
3) Backlash - This is "slop" in the motion system itself. It can come from bolts that aren't snug, play between the nut and the screw, slop in the motor couplings, etc. Nothing in the DIY price range is ever going to be truly backlash free, but since this error adds up over time with each direction change in a movement, you have to control it unless you want a machine to make straight cuts all day.
4) Runout - this is the eccentricity in the router tip itself. An accurate spindle with an accurate collet and high-quality tooling should solve this.
To build an accurate machine, you need to be controlling for each of these. It seems like you saw some things people were doing, and then copied it more cheaply without really understanding what was going into the design decisions.
Here's what I would do with your present design to attempt to fix the material selection and design errors.
1. 1/4" plate alum gantry side plates... 1/2" would be better.
2. Boxing the gantry head... front and back. I'd go with 1/4" alum but that could get really expensive. Steel would be cheaper but heavy... Maybe MDF as an economy solution... but again... heavy.
3. More vertical intercostal struts for the table spans.
You will most certainly be addressing these issues at some point down the road...
Senna
aka BOOMER52 >>> http://www.rcgroups.com/forums/member.php?u=159693
Good thoughts. More structure on the gantry will add more weight. The intercostals will help, but I'd still suspect that another set of legs will be required to bring the deflection into line.
Thankyou gentlemen, I appreciate your input. Yes I am kind of on a budget. No it is not a copy of someone elses. Actually Bear5k alot of design and thought went into this project, and 2 weeks with a design engineer for 80/20 at my local distributor. I have 14 years experience building machines and machine automation for the stone working industry, flawless, but everything there was steel. I admit this is my first aluminum project.
In lieu of this I did order another set of legs for the X axis and but I can only plate the back and the ends on the gantry.
Here is an update on my build...and now if my hellper would just have opposable thumbs.
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