Author Topic: cast aliminium bash plate (Read 14559 times)

shanti · « **on:** May 23, 2015, 11:51:58 am »

busy redoing my bashplate for my bike 07 KLR 650 , while I was at it started to look at my old plastic bashplate and was wondering the different in strength between cast aluminium and aluminium plate . I have a small sand casting foundry here in Knysna casting sculptures for artists and looking at the plastic bashplate it would be a doddle to cast one in ali using the original plastic bashplate as my hard form - it is 4.25mm thick with a 6.5mm thick border on the top . My thoughts would be to reinforce some areas by adding sculpting clay then cast . I cast sculptures which arnt subjected to the strains of a bashplate so have no idea if it would hold up - am I heading in the wrong direction here , any opinions would be appreciated

Crab · « **Reply #1 on:** May 23, 2015, 12:00:41 pm »

The plastic plate has a good shape to work from. Nice rounded surfaces which are better than the angular cut and bend plates.
Try bending some of the aluminum that you have cast and see how it feels strength wise.
It all depends on what is alloyed into the ali you are casting, your stock could be sourced from recycled pots and pans.

RobC · « **Reply #2 on:** May 23, 2015, 12:01:57 pm »

No! Do not diy a cast one...

Cast aluminuim does not have the tensile strenght plate has.
The metalurgists on the group will explain why.

shanti · « **Reply #3 on:** May 23, 2015, 04:45:34 pm »

would love to know why , I find the only brittle areas in the ali sculptures are where they have been tig welded , the KLR bash plate has formed grooves - to make the plastic form stronger , I could fill those and have thicker areas for strength ?

RobC · « **Reply #4 on:** May 23, 2015, 05:38:10 pm »

Quote from: shanti on May 23, 2015, 04:45:34 pm

would love to know why , I find the only brittle areas in the ali sculptures are where they have been tig welded , the KLR bash plate has formed grooves - to make the plastic form stronger , I could fill those and have thicker areas for strength ?

It has to do with the voids in a casting, forged aluminium has no voids and is much stronger than cast. Here is just one of many articles on the subject...
http://www.azom.com/article.aspx?ArticleID=1510

http://sheldonbrown.com/dp-forging.html
"The strongest result is usually from forging. As metal cools, it forms "grains". The grains are strong, but they don't "stick" to each other perfectly. So castings may well break, and if you look at the break, it will show a bumpy "matte" surface, as it will have separated between individual grains. In metalurgists terms, it shows poor ductility."

BTW a bash plate is there to protect the cast alloy parts of a bike engine.

You also need to fit it far enough from the castings you need to protect to give the bash plate room to bend and absorb impacts without touching the engine parts in the process.

shanti · « **Reply #5 on:** May 23, 2015, 06:23:32 pm »

is this not aluminium ? Casting or pressing , not sure

Gérrard · « **Reply #6 on:** May 23, 2015, 06:32:04 pm »

Will be pressed/shaped/rolled. I had to bend and hit my AT plate back into shape regularly. If it was casted it would have snapped.

shanti · « **Reply #7 on:** May 23, 2015, 06:33:09 pm »

with casting I could achieve a more rounded shape - better for deflections possibly , the bash plates I have seen and my previous one are mostly flat planes that take knocks directly - I am all for overkill

you should see my previous bash plate - I figure if I hit something that will break 5-6mm caast ali in a streamlined shape with enough force to break it I am deep shit already , thanks Rob for the heads up - will cast one next week and just check - got some other things to cast next week anyways

Gérrard · « **Reply #8 on:** May 23, 2015, 06:37:34 pm »

Remember, the question is not which is the stronger, bit simply if the casted one is strong enough.

Go for it.

shanti · « **Reply #9 on:** May 23, 2015, 06:39:15 pm »

thanks Jupiter - seems I am going against grain here - I cant help messing with things - started last night to sculpt my angel that will be in the casting - ha ha so much for streamlined shape - her wings will help strengthen the sides - or something

Gérrard · « **Reply #10 on:** May 23, 2015, 06:42:16 pm »

O yes, something else I wanted to mention... lots of big holes to allow flexibility... like toilet paper. Ever noticed it does not break on the holes

shanti · « **Reply #11 on:** May 23, 2015, 06:46:52 pm »

my wings will cover the major holes and I will strengthen around the smaller ones - on a more 'normal' version I would add the clay in ribs to strengthen the plate at the back - keep the front as smooth as possible , anyways obviously making it up as I go along - my previous bash plate was so strong all that could potentially happen when I collided something was my entire frame getting bent , I think a bit of built in redundancy is possibly a good thing

SmuGS · « **Reply #12 on:** May 23, 2015, 06:48:53 pm »

Also remember a bash plates duty is to absorb and dissipate the energy from an impact while deforming, rather than transfer it directly to the engine or frame where it will cause damage..

RobC · « **Reply #13 on:** May 23, 2015, 06:52:37 pm »

Quote from: jupiter on May 23, 2015, 06:42:16 pm

O yes, something else I wanted to mention... lots of big holes to allow flexibility... like toilet paper. Ever noticed it does not break on the holes

My KLR's bash plate has taken dings that have loosend tooth fillings and yet hardly has dents, I am convinced that without it I would have lost a motor casing on more than one occasion. Casting will never have absorbed those blows and stayed in one peice. Fit a proper bash plate of 5mm or more plate aluminium and spend the time you would casting one out riding the bike.

shanti · « **Reply #14 on:** May 23, 2015, 06:56:01 pm »

I will give it a shot next week - not holding thumbs - the ali I cast can bend somewhat ( if I de-oxidize heavily with some manganese ) as some of the arms in the sculptures have to get beaten a bit into shape if there has been a problem in the casting , a few of my forms have been around for a while so always need to be tweaked .

shanti · « **Reply #15 on:** May 23, 2015, 06:57:49 pm »

Quote from: RobC on May 23, 2015, 06:52:37 pm

Quote from: jupiter on May 23, 2015, 06:42:16 pm
O yes, something else I wanted to mention... lots of big holes to allow flexibility... like toilet paper. Ever noticed it does not break on the holes

My KLR's bash plate has taken dings that have loosend tooth fillings and yet hardly has dents, I am convinced that without it I would have lost a motor casing on more than one occasion. Casting will never have absorbed those blows and stayed in one peice. Fit a proper bash plate of 5mm or more plate aluminium and spend the time you would casting one out riding the bike.

Rob - you have no idea how the mind of an artist works - its all good , riding and pottering in the workshop - each both essential to keep me happy

shanti · « **Reply #16 on:** May 23, 2015, 06:59:26 pm »

there must be something to be said for deflection vs brute strength

RobC · « **Reply #17 on:** May 23, 2015, 07:08:35 pm »

Quote from: shanti on May 23, 2015, 06:59:26 pm

there must be something to be said for deflection vs brute strength

The diffrence between deflection and absorbing could be a 100m cliff...

Your old steel bash plate was a better option than a cast one imho as it was able to deform yet protect, a cast one will just break and probably end up piercing the very casing it was meant to protect. I understand the artistic desire to produce something beautiful... but on a DS bike brawn beats beauty every time. Do some reading on metal ductility, it convinced me.

shanti · « **Reply #18 on:** May 23, 2015, 07:19:17 pm »

Thanks Rob - yeah doing some reading too - seems if I cast with an ali alloy I might get somewhere maybe by getting an ingot of 319.0 or 320.0 - will speak to NFS , my previous bash plate took some knocks - luckily it never brought me to a standstill otherwise i would have been over the bars - I always got knocked up ( if I am lucky

) knocked left or right -

GRIM · « **Reply #19 on:** May 24, 2015, 09:08:01 am »

I say go for it

If it works that's great, if not just melt it down and try something else