Anyone got any tips on cutting seat foam ?

[AshimotoK0]

Anyone got any tips on cutting seat foam?  I need to make a new foam for my '61 CB92 project. I do have the remains of the old one ..it's very much in the style of the CB750 sandcast ...i.e. made out of many blocks of red rubber sponge. I seem to remember somebody using an electric carving knife to contour the surfaces of seat foam  but any practical advice gladly received. I am going to make the new one out of a single piece if I can ... hopefully cut from the foam of my old CB500K0 foam or possibly a  nice CB250K0 foam. The 1961 CB92 seat was a tiny and  flimsy affair but an absolute hens teeth item to find in decent nick. I have just learned to TIG weld (well sort of  ) and repaired the steel base so that it looks fairly acceptable, which is a real bonus.

[UK Pete]

I have used an electric knife with reasonable success,  and a fine toothed wood saw as well, I have heard the hot wire method can be used but never tried it, I don't think any of these methods are ideal, and also Wait to here How other people gave done it

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[JamesH]

Pro upholsterer near me uses an electric bread knife and hot wire method..

[K2-K6]

As both above,  work quite well dependant on foam type.

Add one of those wavy bread knives to the pile,  freshly sharpened on a "steel" prior to use.  The scalloped type that is,  as it stops the blade pulling the foam into distortion as it cuts.

One of the best and most effective I've seen was a band saw we had set up with a blade that had the teeth ground off the blade to make it a straight knife effect,  really did cut like butter.

Did anyone see that current series program "Goblin works garage"?  Guy on there "comped" a seat foam shape buy glueing slabs of yoga mat together with contact adhesive,  very cheap effective way of prototyping if not finalised form.  Worth looking at for idea.

[Nurse Julie]

I used electric carving knife and bread knife when I made the seats for our 550 and 750 Mongrels. I used that heavy duty reconstituted foam and it cut well.

[mike the bike]

I modified a jigsaw blade, making the cutting edge thin like a knife, and slightly wavy.

[Tomb]

However you cut it you always end up with lumpy bits that need a slight trim which is hard to do. For this I always use an angle grinder with sanding flap wheel, a worn one is best coz it fair takes off the foam so gently does it.

[Laverda Dave]

Back in the day when I was a coach trimmer we used an Eastman electric reciprocating knife to cut foam, these always had very thin, flat knife edge blades and always gave a perfect finish.  The electric carving knife idea is the closest thing to it, only problem is the serrated blades rip into the foam. Ideally take the blades and grind them to knife edge. You can buy replacement blades for £11 on ebay.

[Rozabikes Tim]

We used those Eastman knives in the upholstery trade. Bloody lethal - hence chain mail gloves etc.

[Laverda Dave]

We didnt have any chain mail gloves, in fact no H&S equipment back in the late 70's/80's!  The only H&S 'regulation' we had then was apprentices were not allowed to use the knives unless supervised! We used to cut through 10 layers of thick seat moquette at once to make the train seat covers for the underground.
I used to do a lot of 'private jobs' during my lunch breaks back in the early 80's modifying motorcycle seats, usually making them into stepped seats as this was the craze at the time.  If you look under my bench in the photo you can see the seat base of a 400/4 I was modifying for a mate.  The second photo shows the completed seat on his yellow 400/4, we were going on a trip to Wells-next-the-sea.  My mate asked me to cut 1.5 inch out of the seat to make him sit lower and to build the pillion seat up by about 4 inches.  I'm glad it wasn't my backside sitting in that seat for for hours on end with very little foam left!
I was on my red 400/4 in the photo complete with a car stero lashed to the petrol tank with speakers mounted into the fairing. The bike handled like a barn door in a gale and would dance across three lanes of a motorway above 80!
Can you imagine cutting up a 400/4 stock seat nowdays!

[MCTID]

I remember at London Underground when you had to go to the Stores to draw out a sharp knife....and if you couldn't produce a Method Statement and a Workplace Risk Assessment, and be able to convince the Storeman that you 'knew what you were doing', they wouldn't issue you with the sharp knife !

That was when 'Metronet' were running the Maintenance side of things and had lots of injuries with people cutting themselves. Another one I remember was placing signage on Staircases which read 'Hold the handrails at all times'......again because we had so many injuries from people falling down stairs - usually because they never held onto the handrails !

Happy days all the same. Just glad I'm retired from it all now. LOL.