Old School Burly Build Gantry Issue

Just finished my Burly build and the gantry deflects a considerable amount if lifted from the bottom. How much play should there be in the gantry? I assume you would want zero play. Is this a known issue so that there is a known fix? Any help would be greatly appreciated.

How large is your build, and what kind of tubes/pipes did you use?

Bed Size: 23"x33" Rigid Electrical Conduit. 23.5 Kit - X Rails: 36" - Y Rails: 38" - Z Rails are 11.5"

The 3/4 in EMT conduit is a bit springy. There are two approaches that most people take, either surface the spoil board so that its contour matches the flex of the conduit. Or, install midspan supports to help keep the EMT level.

The real question would be whether it is causing you any issues. you can check the conduit to see if it is level using a straightedge. You determine how much deflection you are getting as you move the gantry around. This can be done by hand while the CNC is powered off.

Personally, I never bother to with my original build (3ā€™ x 5ā€™ footprint) as it had other issues, and I was almost always through cutting anyways.

I discovered this issue while milling my waste board to match my CNC. It is leaving a ridge on the back side of the cut on every passā€¦ I havenā€™t measured it but it looks to be a good mm at least. At first I thought my spindle was not perpendicular to the table. But then I found this issue.

Sounds like you might have to look at midspan supports then. You can find some models on Thingiverse, such as this:

I donā€™t think you should need mid span supports at that size (but itā€™s your machine, feel free to edit it however youā€™d like).

The 23.5 is not as rigid as the 25.4 size, but keep in mind that you are just bringing a bit through and it does not need to be able to resist a full grown man pushing it around. The forces we use when milling are really quite small, because the bit is just taking a little off at a time.

If youā€™re having trouble surfacing the spoil board, you probably do have a problem with perpendicularity. You might try measuring with this tool: https://www.thingiverse.com/thing:1525661

It is also easy to accidentally bite off more than you wanted when surfacing the spoil board. Maybe you are shooting for a quick skim of 1mm, but you set the zero in the lower left, and at the far right, it might be taking off 4mm at once, which will definitely cause you headaches.

Be sure your bearings arenā€™t the problem though. If you try to move the Z around, the bearings shouldnā€™t allow any slop. The tubes and plastic should bend, not just switch which bearings are touching, if that makes sense.

Thatā€™s great Jeff thanks for the link. If I am able to determine that the spindle is not perp. then what do I do to correct that issue? Also the conduits do not bend. It is when I lift (gently) on the bottom of the z that the entire center moves. The conduit doesnā€™t itā€™s like the bolts are allowing all the parts to move. Am I too loose on my bolts and bearings?

Can you see what is moving when you do that? Like, maybe the top bearings arenā€™t touching the conduit, and when you lift it, the bottom bearings arenā€™t touching? Donā€™t go tightening things without knowing what is loose, but you may need to tighten the tension bolts to make it close up. Or there may be an issue with the actual diameter of the tubing.

It should be close. Small shims in between the tool mount and the router can go a long way. Just some plastic from the recycle bin cut into strips should give you pretty thick shims to try.

Another thing to point out, there is some backlash when you lift the router. The routerā€™s weight is holding that all down. For example, the leadscrew nut can move a little up or down on the leadscrew. Thatā€™s OK, because you have a couple of pounds on the nut, and it wonā€™t defy gravity to raise itself up.

Itā€™s pretty hard to talk about though. Because these are a bit ā€œsquishyā€. Yes, the tubes will bend if you push them. That isnā€™t usually a problem. But there are issues that can happen with the machine (like the bearings not touching) that will cause you issues. But you can also pull your hair out trying to get those super tight (which they donā€™t need to be).

Also, if your nickname is ā€œold gorilla fistā€, thereā€™s a fair chance anything shy of a six figure mill is going to flex when you rattle its cageā€¦

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The wife has grounded me from the CNC until I get some things knocked off the honeydo list. I will report back the minute Iā€™m able to work on it again.

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Iā€™m glad Iā€™m not the only one :flushed:

Kevinā€™s wife grounded you too? Bummer.

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Iā€™m glad my wife doesnā€™t read this site or.i would be in trouble for being grounded by anotheršŸ¤

Yep the wife runs a tight ship around here. LOLā€¦

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