CNC X Axis Linear Motion Actuator – HGR15 Rail Guide

So I’ve finally made it up to the old new studio, and I’ve more or less settled in. I must have gone up and down the stairs several hundred times, but it had to be done. The rooms a lot warmer and drier than the previous space, and the CNC machines look a lot happy here. I do have some footage of the move so I may edit that into a separate video just for the Patreons, but in this video I’m going to focus on assembling an x axis linear actuator for the latest rendition of the CNC machine.

These are Machifit HGR15 rails from banggoods, which I’m planning to use to assemble a basic linear actuator for a CNC X-axis that I’ve designed. I’ve been sent these to review but I’ll also show you how to check them for squares once unpacked, and how to install. These rails are 600mm long, and also came with a couple extra rail blocks – so four in total.

Most rails at this size have two types of rail blocks and the ones I’ll be using on these are the CA type. While the other type you can get are the CC type. CA types use smaller M4 machine screw for mounting, are more box shaped and thicker, while the other type are shallower, wider and uses a thread size up for mounting too.

These could have definitely come better wrapped and I think that’s an issue with buying from banggoods. I’d really like to see them improve packaging for delicate items but that said the rails are quite thick and they haven’t seemed to be damaged in transport.

(back track)

That said they may have manufacturing errors so now I’m going show you how to check them once unpacked.

This is a granite worksurface which cost about £10. It’s pretty flat for the price and I’ve used this for various purposes including sharpening chisels and checking tool flatness. To check your rails it’s quite simple to do. You simple place the rails on the clean granite to start with – checking they don’t rock or wobble. Here I’m looking for twists or bows in the rails themselves. You may need to clean the rails a little to remove any grit or particles suspended in the oil these things are covered in.

Once you’re happy with the rails you’ll need to install all the rail blocks, and using an engineer’s straight edge or the flat surface form an engineers square – check the surfaces of the rail blocks are parallel. Essentially you want to know that the plate you are attaching too onto these four points will not twist out of shape.

Try to keep the rails parallel while doing this, to mimic the actual setup and check the blocks along the entire length of the rails – not just the centre.

These are pretty good. With the thinner rails I’d normally soak the whole block in some kind of spirit to break down the grease and get rid of any particles that may have got in. And then to reapply but I think these are ok.

To complete the assembly I’ll be use two pieces of 20×40 aluminium profile, a single 650mm SFU1605 ball-screw, a FK12 end support, a 10mm to 6mm motor coupler, a Nema23 stepper motor, and some 8mm thick endplates I’ve designed an cut from Valchromat.

Ok I’m jumping a head here. What I’m going to do is attach the plate which will then have the z axis mounted to it. And you can see I’ve recessed all the holes where the profile will run across. Now there’s a procedure to do this to make sure you keep this square to the x axis, and so that the end plates, the one over here and one holding the stepper, are not fighting against how you attach this. And you should start by doing two things. The first thing is making sure is your nut housing is secure and these plates are held in place tightly. Essentially how this travel will inform how the rail will line up. The other thing is to make sure both your rails are loose. So you can see they are moving around. Now the first thing I’m going to do is attach the plate to the nut housing and I’m doing everything on the granite workshop.

This method assumed all the plates have been machined without massive errors from the original vector illustrations – and that plates with openings opposite each other are at least symmetrical. Once the nut housing is attached, I can push the rail block underneath and fit the countersunk M4 machine screws. The hole tolerances are quite high with the M5 holes machined to 5.2mm and the M4 are to 4mm. I’m not overly tightening everything just yet as I want to move the Z carriage plate, nut-block housing and four rail blocks towards the FK12 ball-screw support.

Working from one fixed end should help ensure the pieces maintain alight from the end plate location. You may be tempted to throw a drill at the end and do this quickly, but the chuck can damage the steal, and the weight of the drill could pull the ball-screw off a little as well. Go slow and be patient and you’ll have strong and slightly achy hands by the end of this.

Once the plate reached the FK12 support I back off 1mm, and make sure the rails end roughly in-line with the edge of the rail blocks. I then secure the rail to the aluminium profile on the opposite end of the plate – but not too tight.

I’m going to start by tightening these two here.

I start to back off the plate to I can see the first machine screws on the rail by the end support and tighten these up a little.

Tighten that up a little bit.

Now I’m going to fully tighten the machine screws through the carriage plate to the nut block housing, and the M4 socket screws to the rail blocks.

And you don’t want to over tighten them coz you don’t want to loose the thread and that is possible. They are still just M4 socket screws so the threads are quite small.

Now I’m going to add the remaining…

I’m using 20mm M4 machine screws for the inner mounting holes, plus thick washers. I can feel them bottoming out a little but they tighten up well enough.
I then finish tightening up the machine screws on the rail, working the carriage plate along its entire length from the FK12 end to the stepper end – always securing the rail screws closest to the blocks. Moving along a little and repeating the process.

This process results in the plate and blocks pulling the rails in line as they move along. I can tell that feel really good. The third set of machine screws was the first one I tighten on the rails – they’ll need to be fully tightened now.
I have to be careful not to thread the tee-nut. You may loose a couple and have to repeat the process until you know when to stop.

After that I can add some cap inserts onto the rails to hide the screw heads, prevent grease and dust getting into the openings, and to generally neaten the appearance of the rails. In retrospect I’d recommend putting these on when you have run the stepper motors, and the entire machine is assembled – just in case something went wrong they’re pretty fiddly to remove.
And finally I check the entire assembly on the granite block, and it seem flat and I can’t feel anything rocking.

I’m now using a digital bevel box to check that the carriage plate is flat and is not twisting while moving. It’s pretty good. There’s 0.1mm deviation on the top left of the plate further along but for my purposes it’s not going to be a problem.

I also check along the other direction of the plate and that seems fine as well.

I got lazy here and used the drill to move the plate along.

Ok that looks good.

At the end I’m moving the plate at the full speed of the drill – which is around 1600 RPM

And this is where I’ll leave the video – with some majestic clips of a fully assembled CNC machine performing a homing cycle, moving to the X and Y zero position, and then the probe location when the spindle lowers while performing a probing cycle. If you’d like to check out the parts used in the video I’ll provide affiliated links in the description below. And if you want to support the channel and get first dibs on the manual I’m finally working on which looks great, I’ll provide a link to my Patreon page in the description below. Thanks again for watching and you’ll catch me in the next one – warm and dry.

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