MGN12 Linear Rail Guide / Dial Gauge Jig / Improving Movement / Butting Rails

So I’m trying out these MGN12 Linear Sliders. They’re a bit hit and miss. This side feels really good but that side not so impressive. I’ve also redesigned my plates for my CNC machine, so they’re a bit smaller and use this system. I’m going to have to do quite a few different things to get running. I want to experiment with different methods of moving the plates and I do have some SFU1204 ballscrews which I think – I’ve got an idea of how to fit them within the track to run the plate across. But before I do that I need to make a jig to hold my dial gauge in a particular position so I can make sure the two rails are nice and parallel and I think I’ll be able to use that as well to check how the blocks run as well.

So I’m not going to do anything too fancy. I’m going to 3D print something with the mounting holes and then to make sure this lines up, I’m grabbing my protractor and working out this angle. It looks like 30 degrees.

Ok, if I just back track you can see what I’ve done. I’ve created a new sketch, created a rectangle that’s 50mm by 40mm. I then created the holes using the circle tool and rectangular pattern which you’ll find in the sketch. I offset the hole so that these are in the centre. And then I extruded that, although I forgot to create a new component. E for extrude, say 6mm, new component ok.

I then created a new sketch on the top of the square component that I just extruded, and made an angled rectangle where I wanted the mounting section to go.

I added a contract to make those two lines parallel, and those two lines parallel. I’ve already worked out the offset and now that’s perfectly in the centre, but do I want it in the centre?

I extruded that with a join operation, and on one of it’s faces created a new sketch with the shape and opening for the attachment bolt. I extruded that this time with a cutting operation to leave the desired shape. I then went around with the fillet tool, to round over all the edges and make the jig a little more ergonomic.

Ok just add a bit of strength to this after I’ve 3D printed it I’m going to create some fillets around this section here. Maybe 2mm. Maybe 1.5mm. That should still give me enough room around these openings for the machine screw heads, and maybe a washer.

I also created a recess for the machine screw heads as mine were a little short to attach fully into the MGN12 block.

So this jig will allow me to keep the bars parallel but I’m going to need to make something else to keep this edge of the rail 4mm in from this edge of the c-beam.

Yo can take these blocks off the rail but you’ve got to be really careful not to pivot down or up as you do so, otherwise you can pinch the bars.

This particular block is running really nicely but every now and then you get one which is a bit stiff.

So I need to work out a way to improve this, and I’ve got a few methods I intend to try.

If I turn the rail and block around, you can see the ball bearings. And if I hold the block steady and move the rail what you can see is this particular block there’s no gaps between the bearings. The blocks that seem to stick seems to have gaps in the bearings. Also this seems to like moving in that direction but coming back that way around, I can feel it gets stuck there.

There may be a bit of burr on the metal, or the plastic hasn’t been formed properly, but the only way to find out is to open one up.

Lets take this one apart and see if I can replace the bearings.

I put down a piece of chamois leather and kept a magnet nearby, both of which to help prevent losing any small bearings or screws. I then began the fiddly process of dismantling.

I quickly realised I needed to dismantle a few blocks to compare the pieces. I’m going to take another one apart as well and compare the two, just to see how similar they are.

After checking the main metal block with a calliper, I concluded it more likely to be the balls which was causing me problems. But before I replace the balls I decided to take a bit of wet and dry paper and try round over the ends of the tracks the balls ran along. Maybe there’s a slight burr that I can see or feel.

15.48, 15.47, 15.47, 15,.48

Even though these seem pretty good there was a slight difference in the movement from one compared to the other and I think it’s a dud ball in here.

I also rebuilt one and placed a bit of fresh lithium grease along the track but this didn’t help.

I then remembered a jig that Pocket83 built to help him sort out marbles, and went about building similar but for my purposes.

So this is the jig I’ve made. It’s got two steal bars running along the top of the jig. And I’ve divided the troth into several sections. I’m using playing cards to help keep the balls in the correct distribution so they don’t bounce off into other sections. The problem I’ve found with this is these ball bearings are so small, that they just don’t weight enough to fall down the track by themselves. So I’m having to push them along until it eventually drops into an area. The other thing is because these are so small I’m finding adjusting the bars by hand are really difficult, so what I’ve done is just tension the clamps at the end here ever so gently to try and create a distribution that I can actually see. The first few times I did this I was literally just getting everything landing in either one or two of the trays. So I think the clamp has slipped a little bit. So tricky this. I’ll have to start again. So I got one ball here (by itself) so I’m putting that down again to see if it was an accident and that was.  Ok I’m not getting consistent results despite the bars being solid 12mm steal. I don’t know if it’s the movement of me having to push the balls along that made there pull out a little bit – I can see them flexing even along this short distance by hand.

Because I had the row of cards as a reference I could see slight variations in how the balls dropped but my range was limited to roughly a couple centimetres – the width of the pockets. I could try holding a ruler along the channel, and instead reading where the balls drops against the ruler – by the millimetre. But I’m not sure I have the patience to do that.  I’m going to wait for a jewellery scaled to come in the post (that was crap so I didn’t film it in the end)… What I’ll do now in the meantime, is clean the blocks by soaking them in some alcohol.

So I’ve actually bought extra blocks. They come with this bit of plastic in place and this simply slides off and I can just dump that in. The thing to try and do is move the balls around in the solution.

So after cleaning the blocks you can see quite a bit of stuff has managed to come off. I think this might be the secrete so it’s worth buying a few extra bearings balls – this particular type is 3/32 of an inch just in case you loose some, and if you’re really meticulous take the whole thing apart and soak the parts in some alcohol. I’m using methylated spirit. Alternatively you can pop the whole block in and use a tiny screw driver to just shuffle the balls along until they loosen up a bit and improve. And I think afterwards you apply some clean lithium grease. Not too much because that can suspend dust and particles in it, and return them back to the rail.

I’m going to make another jig now which will help me set the first rail at a fixed distance against the side of the c beam. I’m going to use these scrap bits of aluminium that were actually for the x-carve – to extend the height of the gantry. Made these quite a while ago and I kept them thinking I could use the aluminium. What I’m going to do is use these three points to secure the piece to the cbeam and I’m going to drill a hole in line with the rain which I can pass a machine screw through, which I’ll bolt at a particular length and that’ll be my stop.

This face here is 4mm away from this face or it should be according to my 3D model. And the centre of the rail is 44mm from the bottom so…

I think that’s pretty good in the scale of things.

There’s quite a bit of wiggle room coz obviously the machine screws are M3 and the gap here is nearly 7mm.

I’m going to cut this down so it makes it a bit easier for me to to tighten the machine screws.

Ok the next thing I’m going to do is butt two rails together and see if I can slide the block across them without too much deflection or problems. I can sort feel they’re a little bit like this – it’s barely anything and not super noticeable.

Something is effecting the movement.

I decided to return the dial gauge to the shorter rails. When I check the first rail it was pretty consistent, but then I flipped it over to the opposite side.

The deflection along this edge is 0.15… This is a reminder that the rails are not perfect. Along with measuring against the opposite guide block when fitting the rails in future, butting rails together will need additional work. I then took off the two rails I had tried to butt together earlier, and first filed the edges, return the pieces to test. I also sanded the pieces when they were secured to the c-beam.

This definitely improved things, but I later realised there’s also variations in the rails guides – so some could slide better than others.

I even tried a few other things include shimming one rail against the other but that didn’t seem to work. So really the most import parts to line up are the angle or bevelled sections in the groove – one at the bottom and one at the top. I can feel that with my nail if I just run that along there it’s pretty smooth and if I concentrate in that space in particular that should also help smooth that up.

Eventually I realised the best thing to do was – feel the rails with your fingers nails, and going at them with a multi tool and tiny grinding attachment.

I got some movement across the rails but I think the secret to using this butting method, is to buy all your rails and rail guides, from the same supplier. And if you plan to extend the rails, to do so in equal measurements and to hope that all the parts you bought had been made around the same time, from the same batch – so the manufacturing tool wear isn’t too noticeable.

Anyway this video has really dragged on – and I still need to make a decision on how to move forward. But I’ve already started cutting test pieces for some new plates that I’m designing which I’ll talk about more in the next video. If you want to see the rails and guide blocks I’ve used in this video I’ll link to them in the description bellow.

And that leaves me with the last thing to say which is, thanks again for watching and you’ll catch me in the next one.

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