Thread: Are existing designs good?

Thought I was being creative referring to 'Little OKA', but seeing 'OKAPotamus' - I'm still laughing minutes later.

Printed plastic windscreen wiper shroud would be good for the D2 when it runs. I did wonder about a wooden form and hammer over thin aluminium or stainless.

My D2 has been parked up for a year while I ponder lifting the head. I walked into that world of pain they talk about if you take the exhaust manifold off to fix the whistle, and the studs break. Should have printed a wedge and pushed it between the head and manifold.

Replacing the exhaust gasket on the D1 was a breeze by comparison.

Originally Posted by workingonit

Thought I was being creative referring to 'Little OKA', but seeing 'OKAPotamus' - I'm still laughing minutes later.

You haven't seen it emerge from a mud wallow....

Originally Posted by workingonit

Printed plastic windscreen wiper shroud would be good for the D2 when it runs. I did wonder about a wooden form and hammer over thin aluminium or stainless.

Too many sections on my printer. I think I can just plastic weld or even JB weld mine. Except it's brittle, of course.

Originally Posted by workingonit

My D2 has been parked up for a year while I ponder lifting the head. I walked into that world of pain they talk about if you take the exhaust manifold off to fix the whistle, and the studs break. Should have printed a wedge and pushed it between the head and manifold.

Replacing the exhaust gasket on the D1 was a breeze by comparison.

Mine now has M10 bolts on the end holes. Head was not removed, but care is needed as you're getting a little close to the water jacket for any hamfistedness.

Originally Posted by Tins

Been looking at the D1/2 headlamp retaining clips. I have printed many of them from a design found on Thingiverse, even posted some out to people. Printed them in PLA, PETG and ABS. They all fail. Driving me up the wall. Anyway, I got a genuine one yesterday. I compared it with one of my prints. The two are quite different. The wall thickness of the actual retaining cup is less, the slots for the expansion don't reach all the way down to the mounting plate. I think that my printing is not the culprit, but the design is. They always fail across the line marked by the bottom of the slots.
The original design from TV:
Attachment 189119
My clumsy first attempt at a redesign: ( I already see a flaw, no taper to allow the ball to enter and push the prongs open)
Attachment 189120
I have yet to test fit one, but will.

I know this is primitive stuff for a lot of you. I think though that my point is that just because a design already exists doesn't mean it's good. Doesn't mean mine is either. Still, if at first.....

Try to get some fillet radii on the bottom of the slots and where the tube attaches on to the base plate. Fillets over a few layers are much more stable. The change in shrinkage at hard edges are weak spots for layer failure.

C

Originally Posted by cjc_td5

Try to get some fillet radii on the bottom of the slots and where the tube attaches on to the base plate. Fillets over a few layers are much more stable. The change in shrinkage at hard edges are weak spots for layer failure.

C

Chris, can you expand a bit on that? I'm feeling my way here.

Originally Posted by Tins

Chris, can you expand a bit on that? I'm feeling my way here.

Hi Tins.
My apologies for not getting back to you earlier.

My previous post tried to make comment that angular edges can often develop stress concentrations and issues with adhesion of the layers. As the plastic cools after it is printed, often it shrinks, developing weaknesses at stress concentration points, which can become failure points when loaded. One way to avoid this is to design in some radii in to angular edges, so that the form shape transitions over a few layers.

example1.png

One spot that causes issues is the bottom of slots in the upper tube. You can see that I have placed some small radii fillets to remove the square edges in the bottoms of the slots? The join from the base plate to the cylinder is another obvious stress point, due to the different shrinkage between the two different sized components. I have placed a fillet around this join to transition from one shape to another.

Hope this helps.
Chris

[QUOTE=cjc_td5;3219035]... design in some radii in to angular edges.../QUOTE]

Really great point...now I'll have to go back review a bit of my work.