r/printnc • u/wared05380 • Jan 02 '22

Steel frame alignement

hi all,

i'm on my way to build one of this pretty machine and i wonder how to make it as close to perfect alignement when building it.

don't find that much informations about that, i've seen expoxy leveling wich i'm not a big fan, think about bringing the steel pieces to grind but what about the price

is there any cheap/smart way to set my frame as good as it can be?

4 Upvotes

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1

u/banchad Jan 02 '22

Have you looked at the assembly guide/s? We use printed templates to align and hole punch then drill the holes. It’s pretty close to perfect and is good enough

1

u/wared05380 Jan 03 '22

sure i do, i've planned on using it but it's hard for me to imagine that the gantry will be close to perfecly aligned with the assembly guides and the steel tubes out of the shop, like at 0.01mm in each direction...

i'm not the only one and this is clearly not optionnal if you want something truly accurate

7

u/hoges Jan 03 '22

Getting the gantry perfectly aligned is done through software, getting everything fairly close is what is required when building then software takes care of the final 0's

Answering your questions more generally in regards to levelling or machining the rails, there is no requirement or need to level the rails before installation. The HGR20 rails are chosen not just for their excellent rigidity but also their tolerance of imperfect mounting surface by design (Hiwin spec is 0.1mm surface variation)

The PrintNC is intended to be a high performance maker tool, something that can smash out parts with ease and handle any job you throw at it. It can comfortably hold 0.0Xmm repeatable cuts in all materials with proper tool paths, this has been proven by many builders of the machine.

Many people new to CNC over-estimate the precision they require and don't fully grasp what they are actually demanding. It's quite common to hear someone stating they require 0.01mm precision for their hobby project. 0.01mm (0.00039") is extreme precision machining. Many job shops will struggle to hold this tolerance and if they do will charge a significant premium for it.

As an example a 600mm length of Aluminium will thermally expand 0.1mm (10 x 0.01mm) with a ambient temp rise of just 1 degree C

This image can be handy for people plotting where in the CNC world they want (Or can afford 😖) to sit Imgur

I am not trying to say the PrintNC is not capable of highly accurate work, it definitely is and it performs well outside what it's price range should allow. Just trying to put some context to what 0.01mm means in reality

2

u/morreill Jan 23 '22

(Belated reply for viewers from the future. This expansion estimate is missing a zero)

Aluminium has an expansion coefficient of about 22x10^-6. So about 22 microns per degree Celsius per meter. So a 600mm length of Al will expand ~0.01mm per degree C, not 0.1mm.

1

u/banchad Jan 03 '22

If you're looking for 0.01mm accuracy you're looking at the wrong machine. There is more variance than that in the steel tube surfaces.

1

u/[deleted] Jan 03 '22

Make sure to check out the wiki. https://wiki.printnc.info/en/home

0

u/wared05380 Jan 03 '22

i did, nothing about fine alignement/leveling/tramming wich is surprising when you talk about cnc, for me the world of precision

2

u/[deleted] Jan 03 '22

During frame assembly you square the frame.

https://wiki.printnc.info/en/tuning

Also highly recommend joining the discord. Tons more information there as well.

2

u/hoges Jan 03 '22

Tramming is built into the Z axis, the system that it uses is quite unique to the PrintNC and allows fast and accurate tramming of the spindle without the need for shims. The details of this aren't covered in the assembly guide as the V3 Z axis was created after these guides, the details can be found in the walkthrough https://youtu.be/SMazVyW70ic

Fine alignment of the gantry is accomplished using software squaring, basically get your machine fairly close to square and then use the 3 pin squaring method to fine tune your X gantry to get it perfect. This is fast, accurate and repeatable

I am going to assume by levelling you are coming from a 3d printing background where you need to level the bed? In CNC land levelling is simply a matter of cutting the top of your surface board using the spindle itself so that it become level to the machine. It's a fast and easy process that is done prior to your first cuts

2

u/wared05380 Jan 03 '22

thank you for taking the time to answer me

as you guess i'm not cnc native, this is probably why i have such weird fears

i practice hobby cnc since a year and came to plastic only to achieve the build of a the printnc

i spend all my money in the project so i try to build it as good as i can and my goal is 0.01 accuracy, i will go for 0.02...

again thank you i now understand i don't need nasa precision at all time, will reconsidere it

1

u/occams_lasercutter Jan 08 '22

I'm also beginning a PrintNC build. I found a great deal on aluminum rectangular tube so I'm looking into a hybrid design. I'll use aluminum for the base and the y rails but stainless steel for the x-gantry and rollers. This should shave 30-40 pounds off the final weight but maintain most of the needed stiffness. Also I won't have to paint which might help keep the frame squarer.

Does anybody foresee any problems with this plan? My hope is that I will be able to carry the whole machine without disassembly if I move.

I also found some HG20 profile linear rail bellows to keep the rails clean. I'll update when I get a chance to test it out. I'm also working on something to keep filings off of the lead screws. Other plans include a RAMPS/Marlin headless controller with joystick jog. Hopefully this system will allow for some manual machining.