Shaft Straightness Tolerance?

[john-seaton 0]

Anyone know what the straightness tolerances are for the print head and x/y linear shafts?

For the print head shafts I can put the two side by side and rotate one and see a gap forming between the two and then go away. What's an acceptable amount of defection in the rods before it affects the print?

Are there any tips for straitening them?

Thanks

John

[Dim3nsioneer 557]

Roll them over a known flat surface (I used the stone top of my kitchen counter). If you realise you have bananas, replace them. I think they should not deviate from being straight by more than 0.05mm (assuming a usual print layer height of 0.1mm).

I bought rods from Misumi for replacing the original on my UMO. They are not cheap but very straight.

[john-seaton 0]

Thanks for the reply.

The problem is that I have bent rods in my printer and these new rods are the warranty replacements. Seeing these bent as well I was curious what the acceptable tolerances were to see if maybe these were bent in shipping. These were just rolling around in the box when I opened it so it's possible.

I was going to get them from Misumi before I found out they would be replaced under warranty. Before I do order a set though I want to get these measured with my dial gauge and see how bad they are bent. Rolling them against each other was just my initial test to see how strait they were.

Today I'm going to go source some parts so I can get some better readings with my dial gauge. I guess from there I'll either report back to support that they arrived bent or just order a set from Misumi.

Thanks

John

[john-seaton 0]

Apparently I didn't have the 6mm shafts in my cart so I started looking for those but the BOM says CF53 steel which is apparently 1050 in US standards. Any idea if 52100 Bearing Steel (hardened) and chrome plated would be better or worse?

[john-seaton 0]

The results are in. I setup a spot to measure the rods with my dial gauge and the results are pretty bad.

Of the 8mm rods 2 were .003" (0.0762mm) off, one was .004" (0.1016mm) off, and one was .006" (0.1524mm) off. Of the two 6mm rods one was less than .001 (0.0254mm) off and one was .008" (0.2032mm) off.

I'm pretty sure these were damaged in shipping.

[john-seaton 0]

I received this response from support about the acceptable tolerances.

 

Hi, John,

I'm sorry in the delay getting back to you today, I was waiting to hear back from Ultimaker regarding the specs for those rods. The tolerances on the 8mm axes rods are +/- .0875mm, and the thinner rods have a tolerance of +/- .07mm, so the rods that were off by .003" were within spec.

Hope that helps anyone else wondering what the acceptable tolerances is.

For us non-engineering peeps, that means the total deviation can be .175mm for the 8mm rods and .14mm for the 6mm rods.

Not sure how you get a .02mm layer height with those specs but ok. I don't usually go bellow .1mm but even then i would think you would want better than .05mm.

Edited May 15, 2015 by Guest

[mdelanno 1]

It "only" affects the first layer. After that, the other layers stay parallel to this one. This is one reason why we need a thicker first layer.

[gr5 2,172]

 

@mdelanno understands perfectly. If the bottom layer is .3mm then these errors are very small. These errors will be consistent from then on up so the second layer will be built upon a layer below that varies in thickness consistently by the errors in the rods. But the errors in the rods will be the same amount on the same location above the bed. So you can do .02mm layer (after the first layer is done) even though the bottom layer had .175mm error.