My big shiny knob

[thinfourth]

Yes its a childish thread title.

I am restoring a bacon slicer for the local butcher who will be paying me in bacon and/or steak

Asides from the main issue of the securing bolt for the blade being quite broken after he tried to remove it with a meat cleaver (he's a better butcher than a mechanic) another issue is the thickness adjustment was lost many decades ago so they were just grabbing the end of the mechanism (did i mention he is a better butcher than a mechanic)

So i made a wee project to make a replacement knob

The first step was to design the knob in fusion 360 where i used a canvas to trace around to get their logo which i extruded into the top of the knob

then 3D print it on my prusa 3D printer

Which resulted in a pattern which i painted and then sanded it down a bit to get rid of the layer lines

Then i used some silicone i made a mould which was left overnight after pouring and debubbling in a vacuum chamber

https://www.easycomposites.co.uk/#!...on-cure-mould-making-silicone-rubber-rtv.html

The mould was then sliced open to remove the 3D printed pattern

Then i got some casting resin (about 400G) and some copper powder

https://www.easycomposites.co.uk/#!...sin/toughened-polyurethane-casting-resin.html

https://www.easycomposites.co.uk/#!...metal-powders/copper-metal-filler-powder.html

Poured this into the mould after i put it back together with large amounts of duck tape and let it set

Then pulled out the resulting cast

Then after LOTS of sanding and polishing i got this which on the top it looks like it is solid copper. Also i is quite heavy but not as heavy as solid metal.

The logo is going to be filled in with some black resin to make the logo stand out hence the experiment with a black marker.

If i was todo it again i would use alot more copper powder and i would also degas the resin as there was a few too many bubble inclusions for my liking


Overall it is a technique i would do again to make large knobs, don't know how well it would work for making handwheels with spokes

All the parts sitting on a 2x4 for scale (no bananas were at hand)

And the process is called cold casting metal

 

[grim_d]

That looks excellent.

 

[Bladevane]

Reminds me of the lost wax process but using printed plastic instead of wax. So could you use wax to save you slicing the mould open?

 

[mtt.tr]

Superb

 

[thinfourth]

Reminds me of the lost wax process but using printed plastic instead of wax. So could you use wax to save you slicing the mould open?

using wax in a FDM type printer is a massive pain in the hoop and expensive. Lost PLA is quite popular where yu use a standard 3D printing plastic and then burn it out of a plaster type mould. if i had been casting a solid bronze/aluminium knob then that would of been the way togo

Slicing the silicone mould if you use a really sharp blade means you end up with quite a small flashing on the final cast which is sanded off quite quickly

i could of printed the mould in 2 parts and then coated it in a release agent but i wanted to have a play with the pattern to check it for size and for the logo

 

[Barking Mat]

Nice knob mate.

I'm not posting pics of mine...

 

[thinfourth]

Nice knob mate.

I'm not posting pics of mine...

 

[Farside]

Very nice, but one thing - that logo recessed like that is a muck trap. Would it be possible to embed something in it and seal the surface?

 

[Bladevane]

Thanks @thinfourth. Useful information there.

 

[Seadog]

Very nice, but one thing - that logo recessed like that is a muck trap. Would it be possible to embed something in it and seal the surface?

As the OP said, he's going to infill with a black resin.

 

[500e]

"The logo is going to be filled in with some black resin to make the logo stand out hence the experiment with a black marker."
Interesting how much steak

 

[Farside]

Serves me right for not reading all of it.

 

[Olderisbetter]

My mate used to love looking at the bacon slicer through the window of the local butchers until she reported him to the police.

 

[Barking Mat]

^ @Olderisbetter , I'm still chucking....

 

[Cobbler]

My mate used to love looking at the bacon slicer through the window of the local butchers until she reported him to the police.

Due to the assistant backing into the bacon slicer we have a got a bit behind with our orders.

 

[julianf]

Do any of the 3d printers print somthing that could be melted out of a mould without a load of residue, in the same way as lost wax?

 

[thinfourth]

Do any of the 3d printers print somthing that could be melted out of a mould without a load of residue, in the same way as lost wax?

Sort of

For a FDM printer you can use PLA which melts/burns out with a wee bit of ash also known as "lost PLA casting"

For a resin printer there are resins which leave almost zero ash and is used alot with jewellery normally called castable resin

 

[Agroshield]

A couple of questions if you would kindly oblige.

Can you use an existing object and just cast the silicone around it to make a mould? In metal casting you have to allow for shrinkage but I am guessing in resin, this is negligible.

How strong is the resin with regards to fixing it to a shaft? Can you drill and tap it directly? Does it need a metallic insert? Could you cast an insert into it?

Thanks.

 

[thinfourth]

A couple of questions if you would kindly oblige.

Can you use an existing object and just cast the silicone around it to make a mould? .

Within reason you can take a mould of almost anything

You just need to have a wee think about how you are going to demould it as holes through can object can be tricky

In metal casting you have to allow for shrinkage but I am guessing in resin, this is negligible.

I haven't noticed any shrinkage

But there is some bubble issues as you will get some air in the resin when you mix it

To remove this you can use a vacuum chamber or a pressure pot

However the silicone you WILL get some bubbles in it so i would reccomend get vacuum chamber

However thankfully the potheads have discovered something todo with a vacuum chamber so you can buy them on fleabay for not a huge amount of cash

How strong is the resin with regards to fixing it to a shaft? Can you drill and tap it directly? Does it need a metallic insert? Could you cast an insert into it?

Thanks.

I have not fitted this onto a shaft yet so this is based on some guesswork

Drilling and tapping is fine i think as i have turned it on a lathe to get a flat back.

From filing it i can't see there being much problems for drilling and tapping it

For putting in an insert i can't see that being overly difficult and would probably bring some advantages

 

[Barking Mat]

Sorry folks couldn't resist.... This was in a post related to a politician, but I'm not going there...Oops...