How to cut bristles...

on 10/03/2009, Tim Downie supposed :

Angle grinder - seriously.

...

Hot wire?

Not sure about this, but you could dipping them in a tray of water to the depth that needs cutting off, then let the water freeze. With the water holding the bristles in place, use the sharp knife to cut the strands as they enter the ice.

Second thoughts is to use plaster of paris or polyfiller instead of water.

Tin snips.

dan.

In message , Tim Downie writes

Hair clippers/beard trimmer?

This is my favourite suggestion so far. The bristles really are tough and I can't see that clippers or an angle grinder is going to do the job.

Any suggestions for DIYing a hotwire cutter?

Tim

Dunno about anybody else, but if I tried this, it this would have A&E written allover it in large burny electricuted letters.

A bit of googling reveals lots of home-made foam cutters, which may serve. An example being:

It occurs to me that one potential problem is welding the bristles together, so need to try it first higher up than your final point IYSWIM.

Hmm, I would have thought a cutting disc on an angle grinder would work - but I'm not sure how nice the ends or the bristles would be afterwards (if that matters)

Last time I cooked one up was just with the +12V from an old PC power supply - it'd heat about 8" or so (enough for what I needed) but didn't have enough grunt to do any more - not sure if that'd be enough for what you're doing...

Does it look any better if you turn all the bristles over so the cut ends are at the bottom of the box? You'll get factory finish ends visible again, even if they're not all exactly the same length.

The bottom ends are embedded in a block of plastic so unfortunately, that's not an option.

Tim

That's what I've been doing so far. I am however getting near to "final height" so I'd rather not get it wrong too many more times. ;-) I agree though that welding the rods together might be a problem.

Tim

Oh good. I do like dangerous tools. ;-)

Thanks for the links.

Tim

Freeze to a block of ice, then bandsaw.

Now there's a thought. No access to a bandsaw alas but perhaps some other saw might do.

Tim

I fancy an hot wire cutter might leave the bristles melted and fused together. An angle grinder with a proper wafer thin cutting disk will cut them without heating them up much.

I used to make them for "projects" some years ago. A fretsaw shaped frame cut out of MDF with a push to make switch screwed to it as a trigger. Get a length of bicycle brake cable and unwind a single strand of wire from it. Straighten out the wire by grabbing each end with a pair of pliers or Mole grips. Then pull them apart hard, the wire will stretch very slightly and that's enough to end up with a straight length.

Fasten the wire across the open end of the "C" shape of MDF. Connect it via the switch to a 12V source - I used to use knackered old car batteries, preferably via a rheostat so that you can adjust the current and hence the temperature of the wire.

It used to work a treat for me for cutting polypropylene, polyethylene or polystyrene sheet or rod.

My dad and uncle played with this using my uncle's car battery and a variety of materials (saw blades etc) once. My uncle's car caught fire after a long run two days later.

Probably just a coincidence. . .

PS is anyone else having trouble posting using news.individual.net?

I'm sure I saw one of those 'How do they do that' programs a while ago about making fancy toothbrushes - with the wavy ended bristles etc. They had a large, profiled sanding disc and the initial rough cut brushes were just held against it briefly.

I wouldn't have thought melting the rods together would be much of an issue if you do it in short bursts and 'disturb' them in between...?