3D printing a conrod pattern

[A7er]

I have 3D printed a conrod pattern with my resin printer and the baseplate it will be fixed to with my Ender3. I used the Ender3 for the plate because I am unsure about getting a really flat plate from the resin printer. I will fill the layer lines on the plate and then glue the conrod to it using the raised bosses to locate the conrod. I can then make a frame around the plate for the sand mould, either resin bound or sodium silicate bound. Maybe try both. I still have to work out the best way of getting the molten aluminium into the mould. The conrod is 89mm long and has a 6mm dia hole in each end. Sorry, no rule for scale! The picture with two plates shows an earlier attempt at mounting a different conrod.

[BillTodd]

Looking good

If they were required to be really straight , itd be possible to add a  coupl of sacrificial fillets on the back to balance the effect of the pocket on the front ( shrinkage of the thicker outer section bends the part upward -  I have had the same effect on a part just printed)

If you need something flat, then minimising the cross-section is vital, even if that means printing it upright.

[Alyn Foundry]

Hi A7er.

Is that a pattern half or the whole conrod? With a little thought and registering you can use it to create both halves during moulding.

Place your runner as close as you can to the big end to reduce shrinkage.

   Graham.

[A7er]

Hi Graham.
It is just one half. The conrod pattern is dead centre of the base plate. The base plate will define the size of the flask. Make one side using epoxy resin/sand mix and when it has set remove the flask and hopefully the mould should pull away from the pattern. Reassemble and repeat to get the other side. Glue the two moulds together, one half will have a simple sprue/gateing system and then sit the whole thing in a greensand filled flask in case of spillage. That's the plan, which went a little wrong when after I had glued the conrod to the base with epoxy glue, filled any gaps and sprayed it, the next day the conrod had distorted on the base. It must have been a reaction to the paint. I managed to remove the conrod and straighten it with a little heat. I glued it back on the base, but didn't paint it. It hasn't distorted so I feel ready to make a flask and try a casting. I am printing out a modified version of the conrod that is both halves that have been hollowed with a wall thickness of 1mm. If the print has worked (I will check it in a moment) I can then fill the void with an epoxy putty which should make it as strong as a part printed with PLA.

[Alyn Foundry]

Sounds like you’ve got a plan.   

Having always used Greensand moulding here don’t forget to throughly vent the mould. And use a good “ head “ on the sprue to prevent a sink.

Have you allowed for shrinkage in the pattern itself? Aluminium has a shrinkage of 3/16” per Foot, linear.

  Graham.

[Jasonb]

Been a bit more discussion over on ME if you are interested Graham

https://www.model-engineer.co.uk/forums/postings.asp?th=182134

It will end up a bit like a shell moulding with the two haves bonded or weighted together with no flask around the sand.

[A7er]

A plan? Me? one step forward......!
My prints aren't too bad. There is some distortion but I think I can fix that when I fill them with epoxy. I also printed out some lettering to glue to the cylinder head before casting it. The lettering is 5mm high, as seen from the front, by 1mm thick with a 3 degree draft. Because the lettering is individual letters I had to draw some bars on the back that then made the text a single object, I hope that is clear! The bars are 1/4mm thick and wide. I was hoping to glue the lettering to the head pattern and after the glue had set cut the bars off. This doesn't look as though it will work. It was nice to see such detail though.
I haven't allowed for shrinkage because most of this is experimentation. If I can get it to work properly then I can start thinking about things like shrinkage. The mould will be fed by a sprue at the big end, it locates in the 6mm hole, and vent/rise from the little end. Same size sprue but I will cut a simple pouring basin at the big end before the resin has hardened the sand. The conrod is 90mm end to end and 32mm wide across the big end flanges. The big end is 16mm thick.

[Jasonb]

I tend to stick a bit of masking tape on the surface to give me a straight line and then pick up the individual letters with a sharp scalple dip into a bit of superglue and then place them.

Another alternative would be to mill a 1mm deep slot with a 6mm cutter and print the letters onto a 1 x 6 strip with rounded ends. This can then be glued into the slot and sanded smooth around the edges.

3mm high individually placed

[A7er]

JasonB. That's some nice lettering there, did you have draft on it?

[Zephyrin]

amazing lettering, sharp and clear!

I once did cast lettering with soup vemicelli alphabet...but we don't have the choice of the font

 

[Jasonb]

That was a fabrication rather than something to be cast. . They were done with Slaters Letters

https://slatersplastikard.com/assets/pdfs/AlphabetFlyer.pdf

The proper pattern makers letters have quite a lot of draft otherwise you end up getting sand stuck in things like the top of an "A"

I've seen the pasta used before, I think it was on a generator frame.

[A7er]

I had the student version of Solidworks for a while. That was very good at positioning lettering on a path and adding draft. I wish I still had it. I now use Designspark.

[Alyn Foundry]

Here’s an example of the use of pattern makers letters and numbers. They’re fitted to the underside of our latest creation, the Robinson Oil engine replica.

My technique is to place each letter and use the capillary adapter that comes with certain Super glue products. You can see the pronounced draft angle.

   Graham.

[A7er]

Did you 3D print the letters? What size are they?

[Alyn Foundry]

Did you 3D print the letters? What size are they?

No those are die cast in Zinc alloy. Available in many sizes and font’s from innumerable pattern making supply outlets. The ones in the picture are 3/8” size, sharp face Roman. Also available in “ flat face “ too.

   Graham.

[A7er]

I had both of my 3D printers running today. A pair of conrod halves on the Ender3, and another pair on my resin printer, an Anycubic mono 4k. The resin prints were a total disaster, but it might have been my fault. After printing on the resin printer I wash the excess resin off the parts with water then put them in the curing machine for two minutes. That might be where I've been going wrong. Small parts don't really need extra curing, according to some on youtube. I might have been "over cooking" them. I ten tried another print with different settings to see if I had been over exposing each layer and causing distortion. I dropped the bottom layer times down from 40 seconds for the first 6 layers to 36 seconds. I also lowered the time for the rest of the layers from 2.3 seconds to 1.5 seconds. The print was an even worse disaster! But, at least I now know tha 40s and 2.5s were right-ish in the first place. The photo shows four prints. From right to left.
Ender3 print, solid, useable.
Resin print, hollow 1mm wall thickness, useable.
First failed resin print, solid, scap.
Second failed resin print, solid, adjusted settings, scrap.

The photo isn't very res.
The supports from the second print are at the bottom

[BillTodd]

The resin prints have failed due to the peel forces bending the supports  and because they are quite soft , they don't spring back. 

Try to reduce the cross section of each layer by changing orientation, and/or add a whole lot more supports. If you are using one of the softer resins, try slowing the peel (lift) speed.

It may be better to print it vertically (or as near as possible)  . Hollow out the solid bits and provide vents where there's any chance of a suction cup.

Understanding the peel forces is critical.
Bill

[A7er]

Thanks for the advice Bill. There is much I need to learn about resin 3D printing. I never thought about trying a vertical print, I will try tomorrow.