Hello Community,
Have you ever tried to mill out a PCB board with SN2. Phhh some kind of struggle and the initial result was not so good.
1st try well totally meaningless, the CNC bed is not 100% flat and there is no means to auto level with the mill. So just imagine the result.
Well, then I purchased a flattening mill. With that mill, I removed a nudge from the spoil board and the result was somewhat better. PCB board no. one perfect result. Happy happy. PCB no 2, not so perfect because something changed? Not so happy anymore.
However, there is some flex in the Y axis. I assume this has been heavily discussed in this forum back and forward 100 million times.
Well the flex in the Y axis is no concern for me for the part I do with 3D printing. But for the PCB milling it is quite annoying,… especially when mill number x goes sideways and well I just need some more rugged plane.
What to do. Examined this forum and found out for the A250 there is no room to do the A350 mod with placing linear rails on the side. So why not try to set one in the middle. I have nothing to lose, SN2 need some improvement. Because I like the machine with this 3-1 function.
See attached picture and my question to this forum, I assume there is some people that has some better knowledge in this matter than me.
My idea: drill some holes in the bottom plate, (why not cannibalize the machine, I do not mind) fit one aluminum extruded 2020 or 3030 rail.
On top of this rail: fit one linear rail with 2x blocks. These Chinese made linear blocks is dirt cheap
Fit the block to the platform with a PETG printed bracket. (less shrinkage and heat resistant)
And somehow adjust the whole chabang into one aligned unit with a dial indicator and shims washers.
Q1: is this the worst stupid idea you ever head of? You have another suggestion
Q2: linear rail or the type of linear rail that is round SRB?
BTW: the 3D model needs some more tweaking, just now a sketch…
Best Regards / Sander
2 Likes
Seems reasonable. And yes, the flex in the bed makes CNC (at the extremes) almost impossible. Doing small CNC objects in the bed center don’t seem to be an issue.
I have been thinking about the same thing for quite some time, but have tried to run two rails between the Y-axis because the A250 does not have the space to mount rails compared to the A350.
In the end, I had to give up because I had to make modifications such as drilling holes.
The CNC machining caused considerable deflection at the forward and backward ends of the Y-axis.
We have confirmed that a light push by hand, measured back and forth, causes a sinking (deflection) of up to 5 mm in the height direction.
CNC machining can only achieve dimensional accuracy of about 50mmx50mm items at the center separately.
I believe your center rail will improve that somewhat.
Please shape up and share!
I think it would be wonderful.
Hello,
Agree “Shape up and share” Love this.
Well progress so fare. I quickly realized that to succeed in this. I need to make a 3D assembly of the A250. So now I’m drawing everything and I would assume 2-3h work left from this reverse engineering.
But today Christmas. Nothing will be done for a couple of days. Assume I can post the A250 model in next week
Brgds Sander
It is great to share this information with everyone.
And if we can make new improvements based on that information, even better!
Ho ho ho, Merry Christmas
Attached Step File of the A250 Modification with linear rail in the Y-Axis. Rev 1…
I indeed need some inputs from the community. I can clearly see that this will be some kind of struggle to build. Using MGM15C rail / slider with a 3030 extruded aluminium, T-Nuts and special made L-Angle. No way I will put myself in the situation to do this, so I will try to draw a second sketch and in this sketch i will use linear rod instead. Problem with the A250 is the connection boxes for the CAN bus. if there is possible to relocate those to another place, life would be much easier. Secondly. linear rod has a bigger footprint. phhhh
Anyhow, the step file is “almost” identical in measurements to the A250, well a few mm here and there, but for this junk I em doing it is more than enough. Model is done i Creo 7. And I do not have fusion 360 as everybody else, sorry. but I assume there is possible to save as somehow if someone would like to “help out” tinkering.
sm2_mod_asm.zip (1.2 MB)
Brgds / Sander
Hello Community,
Ok, well in addition to previous post. now i have re-drawn the A250 with linear rod instead. seriously much easier to install this compared to guide rail. Placed one order for an SBR20 with 2x sliders. the items is expected to be at my doorstep around end of Jan, so until then i will just re-arrange the cable boxes X and Y. need to make some sort of a holder somewhere at the A250. will be fiddling around with this. Attached is the mock up. and if someone need the Creo 3D files just give me hint.
Cut from the side of the A250 with linear rod. The Bottom plate in max position backward -Y
Cut from the side of the A250 with linear rod. The Bottom plate in max position forward +Y
Here you can see that i have removed the two small connection boxes.
Finally: attached the Step file of everything. sorry same file name as previous post but this is the new one.
sm2_mod_asm.zip (1.0 MB)
Brgds / Sander
3 Likes
Hello,
Ok some minor updates. received the SBR20 linear rod from Alien Express, as expected the finish is what you pay for. The rod was greased with a really nasty smelly oil. phh that odor. I’m not joking this was something else beyond I do not know, un-human! After some cleaning and removing burrs from the original cutting with the Dremel I just placed out the rod. se below picture.
Moving the Cable Boxes X and Y was no problem, just printed out one bracket, and rearrange everything.
Here you can see some kind of preliminary mock up. The blue thing is supposed to be fitted underneath the plattform and hold the SBR.
Last picture below.
Well after mourning all the day I realized, either to grind away the embossed text. But that means the Snapmaker will be a Sn ker, and then everybody knows what i have done. Best option is probably to grind away a few mm in the lower aluminium part of the linear bar. Less work
Do not know more just right now the smell has made short circuit in my brain for today. Will return when the my new dial indicator arrive.
Brgds / Sander
Feels like I’m talking to myself.
Anyhow, This took like 2 seconds. Felt little nasty to destroy the machine. We’ll just do it.
Next destruction of modification.
Drill holes and tap M5 holes.
This took around 1h. Pretty much straight forward.
Lastly. Mount the SBR. All in all. Around 2h of work. Measure twice, cut one. Next is to print brackets and final assembly.
3 Likes
Ok, done.
Less work then i anticipated. Result? I tell you what! rock solid Y axis. 
You need to print out some stuff. The holder/bracket for the CAN bus boxes and the SBR block holder.
Will poste theses solids at thingiverse. But absolutely need to fix one solid first, found one stupid error.
Anyhow, Bill of materials:
1x Box of patience and one bag of enthusiasm
1x SnapMaker A250 with bad Y-Axis
1x SBR20 500mm
3x thingiverse printouts use PETG, for the heat plate and minimal shrinkage
6x M4x6 Screws (For SBR Block Holder)
8x M6x16 Screws (For SBR Block)
10x M5x10 Screws (To fit the SBR rail)
Shims, see text below 0.1 / 0.2 / 0.3 mm
Assembly! slowly tighten all screws for the rail/SBR. If you placed the SBR carefully it is 35 mm between the linear rails. see picture above post 9 you can see that i used a couple of small distances with exact 35mm. used those to adjust the SBR bar in the middle of the bed. You also need to adjust the bar in Y-Axis. mine is sticking out 70 mm but it is 515 mm long. Used 6.5 mm holes in the aluminium bar.
NOTE!!! just look underneath the SnapMaker bottom plate, you can see it is reinforced with walls you do not wan to drill into one of those, I put my screws at a distance 2.5 / 10.5 / 20 / 29.5 / 41 cm “Isch” well tanke note…
During assembly I found out that the SBR block holder is 0.3 mm to thin, used some metal tape to adjust this so gliding everything smooth.
Proposal for you is to use real shims washers. the Block has M6 thread. so you need a couple of 0.1 / 0.2 / 0.3 mm
I will adjust this later, do not trust the tape in the long run.
So all in all
4-5 weeks delivery time from Alien Express. Phhhh.
1h to fit the SBR including drilling extra holes. this includes to drill and / thread the bottom plate
16h to print the SBR Bracket. 100% infill. just mentioned this
1 h to fit and assembly the stuff.
I will post the solids later this week. have no more urge to fiddle around in 3D today.
Brgds / Mikael Sander
4 Likes
Hello,
Last Post here is all files.
Brgds
2 Likes
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