Belt Tension Idea?

I’m a new owner of an X Carve and have been working through some of the basic issues
of a new owner.

One issue is the belt tension, but I have an Idea and was wondering if this is viable.

If you put a precision compression spring ( about 4 pounds) at the end of the tension screw
(between the nut and the end bracket) would it not keep a constant tension on the belt?
You would not completely tighten down the clip on the insertion nut.

I’m I thinking this through right?


You can use frequency too.
if the sound is the same then they are a close match.
If you have an I-phone you can get an app to check the frequency.

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The more I read the more I chuckle - you can tell who the folks are who bought toys versus tools. I think of a buddy of mine that has a 3d printer - he’s rebuilt the thing twice now, and is looking at enough additional mods to require a third complete rebuild. I’m still waiting for a printed sample he was gonna run me two months ago.

Get it to where it runs decent, doublecheck everything after initial run-in and don’t fix what isn’t broke from that point on. If you find yourself running everything with 1/4" bits and want to switch to heavier belts, or chains, or screws then sure - tear it down and rebuild it. Your use justifies tinkering time. If all you’ve managed to do so far is improve on the design, put it back together and MAKE SOMETHING!

BTW Gregory: congrats on the purchase. Do what works for you and make some chips. Close counts until you get a feel for the machine.


Well if everyone had the cash they would buy a professional system where you do not have to mod it for use beyond hobby…

ok Most people. :stuck_out_tongue:


Yep, neglected to pick up the scale… Had them set to similar “sounds”… Well, made a couple minor things… Tried a 7 hour project to come back to half of it done, and a large vertical line almost down the middle of the project. After doing some cleaning up tonight, I noticed the top belt had snapped. So… Ordering a scale, and some more belt and learning from my mistake.

Mirrors my experience exactly :slight_smile:

So, after swapping out the snapped belt, and set all three with a luggage scale this time, it is back up and running. :slight_smile:

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Here’s a belt tension gauge tool design I’m working on.

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No idea what it does… but I like it!

If you’re able to stretch that much, it is to loose what I can see.

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Yep, I don’t have them set quite right.

@RonSabourin I wanted a tool that could quickly and easily tell me if the tension was set correctly. Also that i could adjust while it was installed. Its a spring with a known spring rate and calculating the deflection seen by the tool I can determine the tension. Currently it’s set to read 5.1 lbs.

Very cool. Is it affixed to the rails all the time? or just when you feel you need to check the tension?

Just when I want to check it.

Thanks Phil. I have the math worked out and I expect it does what you say. However I realize that wasn’t clear from one picture and a few lines. I just ordered a new scale that i plan to validate my theory with. I plan to do a much better write up this weekend if all goes well.

PS I’m a mechanical engineer by trade :grinning:


There’s an error in your thinking that everyone seems to have missed.

The four or so pounds at one inch displacement everyone is referring to is at right angles to the line of the belt. Applying trigonometry yields an inline belt tension of around 31 lb.

For the reason stated in the next reply, a weight would be the right choice for a constant force tensioner, and it should be 31 lb.

Have fun! Sounds like too much monkeying around to “fix” what’s not broken. :wink:

A simple, relatively concrete spec in the instructions instead of pluck it till it sounds kind of like a bass string (assuming someone knows what that should sound like) would be a good starting point though. :smiley:


unless you have non standard belts the proper tension is this
6.25 lb / 2.8kg Working Tension
So if you supply this to the belt it should be fine.
So 5LBS tension is just less and should work fine.

You know, I’ve never used any scale on my belts. I just tightened them up to where they felt sufficient; judgement call I suppose. They ‘twang’ when I pluck em, so I figure that’s good enough. Been working fine for 5 months…we’ll see how long they last.


So THAT’s what causes those extra lines and curves! :wink: