Bearings, inserts, nuts and shafts

With the 3D printing out of the way, attention can now turn to starting to assemble all the parts of Sawppy. I already covered the aluminium extrusions which link the parts together, but there are various other bits of hardware needed to keep everything together.


Anywhere where there’s a shaft, this project uses inexpensive 608 type bearings (the same as found in roller skates). There are 30 of these in total, which are a firm press fit (or slightly firmer tap with a hammer) to install.

Heat-set brass inserts

Now these things are fiddly to work with. The idea is that you melt them into holes in the plastic to give nice threads for your bolts, here’s just how small they are.

I had an impossible time trying to get any of the exact inserts over here in the UK as specified in the build. The inserts from the build appeared to have a diameter of about 4.8 mm. The only ones I could find are about 4.3 mm.

Unfortunately this means that the holes in the parts I’d already printed were too large for the inserts, which just dropped straight through! I really didn’t want to reprint a lot of things, so I created some plastic inserts to fit into the existing holes but now with a 4 mm hole through the middle.

A dab of glue and a tap with a hammer and I’m back on track. Here’s that part in progress, with the original hole at the front and a new finished one at back right.

Now it’s ready for the inserts. Here’s where I was glad I had a backup soldering iron handy as my trusty old Maplin (may they rest in peace) temperature controlled iron has finally popped its clogs (hence why you see 2 irons in the picture below).

So the idea is just to pop the soldering iron on top of an insert balanced over a hole and it just sinks slowly into the plastic with a little bit of pressure.

It took a few goes to get into the swing of this, but 68 inserts later and I’m done. A little bit of cleaning up of any displaced plastic so I can install bolts and they’re complete. Hopefully these are going to hold when I start to tighten things up.

M3 nuts

For places where I’ll be bolting into the aluminium extrusions, M3 nuts will be used. Roger’s been especially clever here and designed some 3D printable spacers so that I don’t have to fiddle about trying to line the nuts up with the bolts, which is awesome.

There’s 12 of the long ones and 88 of the small ones. Luckily they only took about 2 hours to print for the lot of them. Here’s what one of these looks like with nuts installed and slid into an extrusion. There’s even a handy little tab in there so you can easily adjust the thing.


Finally there’s a need to manufacture 14 shafts in 4 different sizes, which has probably been the hardest bit of the project so far.

Firstly because I wasn’t paying attention, I accidentally initially bought some stainless steel rods. After burning through about 10 cutting discs and spending an hour getting just the first 4 shafts prepared, I re-read the instructions and realised that either Mild Steel or even Aluminium would work for our needs.

Having got upset with the difficulty of the stainless steel, I opted to use aluminium (3 x 300 mm lengths) in order to give myself a bit of an easier time.

These shafts all need slots cutting into them so that E-Clips can be installed to hold them in place. This would be easy if I had a lathe, but I don’t. So I first need to make a ‘Poor man’s lathe’. 10 minutes later and I have one by knocking my pillar dill onto its side and getting out my dremel with a cutting disc attached.

At this point, I was actually rather happy that I had first failed with the stainless shafts as I realised that even being careful with my measuring, I still made mistakes. Back to the printer, I quickly churned out some tubes with the right spacing that I could just pop onto the the rod.

The first two finished shafts showed that this seemed like it was going to work well.

A while later and I have the full set (I can’t remember how long it took, but the sun went down at some point). Apart from a bit of a panic with the final shaft where I went down right to the last millimetre of rod, we’re all done!

Well, I say I’m all done, but there’s just one final bit. Some of these shafts need flats cutting into them to stop them slipping when grub screws are installed. A quick bit of a work with a file sorted that part out (and I was thankful I chose to go with aluminium here too).

Phew. Ok so as far as I can see, that should be all of the prep work done. Now I can start to look at the mechanical assembly and start to see this thing take shape.

Costs so far

Up to this point the largest cost has been time, but in monetary terms for all the parts so far, we’re running at a total of just over 90 GBP and I’ve still got a couple of hundred metres of PLA plastic spare.

ItemQtyTotal cost
Aluminium extrusions2£16.52
1 Kg spool of PLA3£44.85
608 bearings30£14.96
Heat-set brass inserts68£2.92
Aluminium rod 300 mm3£11.97

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