Rango - Build diary

**Mega Masher** · 15th March 2014, 17:48

Wow, thats awesome

**PJ-27** · 17th March 2014, 09:41

How did you cut the HDPE so neatly?

**Ellis** · 17th March 2014, 10:09

A display model tablesaw and hand tool love. :P

**PJ-27** · 17th March 2014, 10:32

Nice! Did mine with a circular saw but don't look anywhere near as good.

**Ellis** · 17th March 2014, 10:51

The finish on the cut surfaces isn't great. I had to use a non-factory edge for one of the sides and so I just tidied that up with coarse grit sandpaper as best as possible. It doesn't match the other side but, being white, happily all you really see is general white, they only feel different. As long as no one rubs my robot it should be aight. :P

**overkill** · 17th March 2014, 11:44

Even a small table saw with the right blade will cut plastic very neatly. I found that a thin kerf blade with a low tooth count meant for ripping wood will cut thru PE, polycarbonate and most other plastics like they were air. The only problem is that the blade will vibrate and leave a somewhat rough edge. If you use a carbide tooth blade with a thicker kerf and still a low tooth count, you can get almost a mirror polished edge, but you need a bit higher powered saw. The secret seems to be avoiding any friction from the sides of the teeth, so using a fence to keep the cuts straight is a key feature.

**Ellis** · 17th March 2014, 12:07

The overall dimensions are accurate enough with just the regular sold-with blade. The finish is a little rough, and it bites quite easily, but in terms of being close enough to CAD for it to work it does the job. If the finish bothers me I tidy it one way or another. Sadly HDPE just goes gummy and nasty when using fine-finish (fine grit sandpaper for eg) methods, the coarser the clean up often the better. I used a fence for the long cuts, which was a piece of wood clamped to the bed, spaced 6cm from the blade in this case.

To drill the holes I clamped the HDPE pieces to the alu bulkheads and transferred the positions, then used woodworking bits to do the counterbores/sinks etc.

Don't have time/need now, but after the champs I may look at getting a different, more suitable blade for the tablesaw. Intend to work more with nylon as I can source it easily, and from past experience that doesn't cut too nicely with the existing disc.

**Ellis** · 21st March 2014, 18:05

Some progress. I've cut and partly bolted on the 12mm HDPE back armour. It is currently only bolted to the outer armour (with barrelnuts, for the curious) as I'm reluctant to put many attachment holes in the alu bulkheads until I have all of the width-dictating elements in hand.

Have also done a bit with the base. It isn't structural, all it has to do is keep the electronics in, thus is it just 1mm titanium. I had already cut the wheel cutouts but had to make them much wider to accommodate the (more recently decided) 2" wide wheels. It is also only attached to the outer panels for now. This is done with some inserts I made, which are M10 on the outside with an m6 thread down the middle. Point being I can bash the bolts in and out without wearing out the HDPE and, of course, it's much stronger than that, whilst still less faff than more barrenuts. The coarse thread of the M10 holds well in the plastic - I got the stiffer variety of HDPE with this in mind.

The wheel bodies are only in the pics for mockup purposes, they need a fair bit more work pulley-wise yet.

Said pics:

One of the inserts. They are 12mm long. No idea how they will work in the long run but they have already made life easier dis/assembling.

In profile, showing the barrelnuts (I found some black ones, was so chuffed about that! :P)

Right way up, showing the back.

Jeroen is busying away with the machining for the drum, and Mario is in talks with a company local to him to get 3.2mm hardox watercut for the wedge. Cutting it tight!

Cheers.