Thread: decided to make one

Thanks again for sharing,

I have no experience with molds used in this way, are they coated with a release agent prior to the two coats of epoxy? Do they tend to slip on each other if not indexed together somehow? Is the bulk of the resin injected while under vacuum, or painted on prior?.Is timber suitable for building molds.

I appologise for getting off topic, rest assured the entire build is fascinating.

Tim.

Originally Posted by Thunknker

I have no experience with molds used in this way, are they coated with a release agent prior to the two coats of epoxy? Tim.

yes , the better the finnish on the mould the easyer it will release , i use a "blue PVA" release as the better epoxys eats "wax release agents" used in fibre glass ,

Originally Posted by Thunknker

Do they tend to slip on each other if not indexed together somehow?Tim.

yes getting it to layer nicely with out cutting corners or falling in on its self is an art , the use of thumb tacks out side the mould area helps and an asortment of sticks in corners to hold everting inplace while laying in the next layer helps , just move the sticks to the top layer as you progress ,

Originally Posted by Thunknker

Is the bulk of the resin injected while under vacuum, or painted on prior?.Tim.

im using "wet layup" ,just for speed and ease , on this project , so the resin is painted on each layer , layed in dry then brushed over with resin , each layer

"Infusinion" would produce a lighter stronger lamination but a lot more work , more suteable to muilt runs of a mould , if you get the infeed tubes or out feed tubes wrong you can end up with a dry spot ,normally takes me 2-3 go's to get the infeed and drains in the right places ,so wanted to avoid a stuffup

Originally Posted by Thunknker

Is timber suitable for building molds.Tim.

well anything is sutable , MDF is not the best , it has to be sealed completely ( i will have to distroy the mould to get this one out )
i have used plaster before , but only get 1 cast of it , pulled the resin sealent clean off the mould when i stripped it
engenering wax would work well no sealent needed but no good for heat

fibreglass polished moulds are what i use for my violins , and its still quite hard to remove from moulds ,on my neck moulds i found that freezing and placing under hot water soon gets them apart ( sheer force distroys the mould ), water gets between the mould and CF , when it freezes it expands , under hot water more water gets in , 3-4 freezes pops my violin neck moulds

all these are only good for room temp cure resins , the real light pro resins need heat to kick the hardning process , polished aluminium is the only mould matirial for that process

with wet layup you have to be quick , all done and under vacuum in less than 3 hours , with infusion you can take a week to set it up for the resin stage but need lots of tubes to allow resin , and out ,
with the pro resins , you bye the fibre coated ( perfect amount of resin ) then layup the mould , you can spend a long time laying the mould up , when your ready you put it under vacuum and heat to finalize the cure ,there are no extra tubes in the setup to fail , a lot quicker and more consistant than infusion but not easy for the back yarder , the pro stuff has a shelf life of 6 months ( in a fridge )

cheers ken

,

i just came up with a thought , and it almost hurt

a lazer defection meter

i have a USB muilti controller with lots of 8 bit DAC/ADC's
i hear you say
a USB board that converts 0volts to 5 volts into 256 steps , so 0volts gives a value in windows (VisualBasic) of "0" and 5volts gives a value of "256"

a lazer line 2.5mm wide shinning across the back ( and bottom) of the y axis onto a photo censor can be ampafied to 5volts , a "beam blocker" mounted on the z asis frame will block the light when the y axis flex's , with a bit of testing and some maths the output on the screen ( progress bar ) will show how much the y axis beam is flexing ,

for a guide when test running g code to set the feed rates v's accuracy
just adding a pause at a direction change ,allowing the flex to straighten before going ahead with its code might increase accuracy alot

2.5mm beam , no flex centered on 1.25mm ( 1/2 the beam , a grub screw used to block the beam ) will give you 125 steps of measurement in both directions or 1.100th of a mm incrament ,

a tube over the light senser to stop stray light getting in , or use a sensor that only acepts the right colour light
an analog amp to increse the light sensors output and adjust to 5v max
into the USB multi controller , windows will have to "ping" the sensor at set time intervals to get a reeding , and display it as a progress bar or windows slide bar , or rolling number ,
electro magnetic stray fields will afect it pritty badly , would have to wire it up on the oppisite side than the motor supply cables

ill build the cnc machine first

Thanks again,
This is on my list of things I would Love to play around with but not sure if I'll ever find the time.
Sadly this list seems to grow faster and faster, But given the right project and funding it may happen.
Anyhow looking forward to shaking you by the hand along with the others in Cairns.

Cheers,

Tim.

Hi Ken, this is slightly off topic but I have a question about epoxy's.

I need to pour an epoxy base onto a concrete base that I have already poured for my next router to bolt down to. What I am after is a dead flat surface, kinda like those epoxy surface plated the Nascar guys use...but on a poor mans budget

I was going to use the thinnest epoxy resin I could find but could you maybe suggest anything that might work well, or better. I think I am going to use about 10 litres of the stuff, the finished layer will be about 5mm thick and needs to have reasonable compressive strength as the machine will bolt down to this in 15 places. The dimensions are (very) roughly 850mm by 850mm.

Any advice appreciated.

Cheers.

Russell.