Mercedes-Benz W165 Grand Prix engine in 1:3 scale

[Vixen]

Hello Jason and Charles,
Thanks for calling in and offering such good advice

Good to see some progress Mike.

Unfortunately, both energy and workshop time are at a premium these days and availability is no longer guaranteed.

Jason, I think you are as quick with your 3D Alibre as I am with 2D AutoCAD. The 'airfix' layout is exactly what the 3D printer people had in mind. They gave three tips,

1.  Make the central spine 1mm wide by 2mm tall. Tell the printer that the spine is sacrificial and they will add heavy duty supports to stop the long thin spine from warping.
2.  Make the side runners from the spine to each spring retainer 1mm wide and long enough for your cut off saw, say 1mm long.
3.  Separate the individual components by 1 or 2mm to prevent them inadvertently fusing together.
4.   A small radius on every edge is better than a sharp edge.

An additional thought about multi-part printing. A 8 x 2 matrix would need four prints, a 11 x 2 matrix would need three prints and a 16 x 2 matrix would only need 2 prints. It would be interesting to see how the prices compare.

Here is a screen grab of my spring retainer. I though to join the side 'runner' into the 0.8mm wide outer edge of each spring retainer rather than onto the end face. The 'runner' only serves to stop the parts falling off during clean-up.



Thanks once again for all your help and advice.

Cheers   

Mike

[kvom]

I would do these on a CNC mill. 

Model a rectangular bar with an 8x8 array of parts.  Stock should be thicker than 3mm.  For each part mill the outer radius, the counterbore, and the center hole.  Fill the spaces around each part with Devcon epoxy.  Reverse the stock and face it to 3mm thickness.  Then mill that side of each part.  The epoxy holds everything in position.  Finally bake the stock in the oven to release the epoxy.  Terry over at HMEM uses this technique for 2-sided parts that need machining.

I've done this myself, but had some difficulty removing the epoxy afterwards.  Learned that I needed to separate the parts while still hot.

In theory this should avoid any per-part finishing assuming you can machine the rounded edges.  With printed parts you'd need to cut off the runners and finish machine where the runners were attached.

[Vixen]

Hello Kirk,

OK, that's another good way to make the spring retainers. I've seen Terry over at HMEM do 2 sided parts that way, but I've never tried it myself. It's always good to have several options available.

Do you know which make/grade of epoxy works best.

Cheers

Mike

[Jasonb]

Just seen the drawing, give me a while and I will see what I can do. Th eAirfix did have 1mm x 2mm spures. And the prices I quoted were for a 4 x 4 pattern of 16.

How critical is that 3mm hole and 6.5mm pocket for the screw. I have found holes come out approx 0.2mm small, just right for reaming. But if you want minimal work then the model should be 3.2 and 6.7

Regarding cutting from flat stock on the CNC. I would use thicker stock so they end up attached to a thin sheet like pills, cut them up with a saw and then just hold in the lathe to face off the flange to thickness.

[Jasonb]

So these are as per your drawing. Joined by 2mm x 0.8mm sprues. 16 in a set so four sets needed to give 64 parts for the two engines.

Craftcloud are quoting £62 so just less than a pound each for stainless.

let me know if you want to try any different sprues or layouts.

[Jasonb]

Same price if I do a 2x1 sprue down the middle and 1mm x 0.8 side sprues

EDIT

If I do 9x2 to a strip so you have some spares it still comes out at £62 for four sets and that is from ProtoTi who we have use dbefore.

[Vixen]

Well that was quick and painless. All 64 spring retainers plus 8 spare have been ordered via Craftcloud. They are due for delivery an about 2 weeks, most of that is shipping time. All that for less than one pound per spring retainer.

It goes to show that multiple small parts can be 3D printed very economically if you nest them together to form one large item, looking like a sprue from a plastic (Airfix) model kit. If they were printed individually, the cost would have been close to £200, not £62 for the nested version.

https://www.modelenginemaker.com/index.php?action=dlattach;topic=5142.0;attach=185941;image

Thanks to Jason for kindly making the STL file in record time.

Mike

[Vixen]

Just 12 days after placing the order, a small package arrived on my doorstep. Inside were 72 small spring retainers, beautifully 3D metal printed in S316 stainless steel. The individual spring retainers were each connected to the central spine by 1mm square runners. This proved to be a considerable saving compared to printing the same number individually.

I uploaded the STL file to Craftcloud (a clearing house for the 3D printing industry) I then selected the cheapest quote from the list. The printing was done by 3DSPRO based in Hong Kong. Actually, the printing costs were lower than their minimum order price of $35 by a small amount, add to that $15 or so for shipping.

3D metal printing proved to be a quick and easy alternative the attempting to mass produce them from round bar stock or milling from 3mm plate. As you can see, the intended valve springs are a perfect fit over the spring retainers.





Happy, happy   

Mike

[Jasonb]

Happy they turned printed out OK.

It won't be long until we will be buying "casting kits" as a tree of 3D printed parts or maybe even just a download. That won't please those that spend all their time Fondling Castings

You can see it already with AFV and figure modeling, even RC planes and boats can all be had for the price of a download.

[Roger B]

Very nice    The world is changing 

It is interesting to look at the changes in model engineering. When it started out as specific area most practitioners had a basic lathe and hand tools. A bench drill and a grinder probably came next. Castings were an integral part due to the limited machining capabilities. The first non industrial milling machines and better lathes then arrived followed by the Chinese machine tools and CNC. Now we have various forms of additive machining. Nothing is permanent but change 

[Sanjay F]

Happy they turned printed out OK.

It won't be long until we will be buying "casting kits" as a tree of 3D printed parts or maybe even just a download. That won't please those that spend all their time Fondling Castings

You can see it already with AFV and figure modeling, even RC planes and boats can all be had for the price of a download.

I'm surprised places like Stuarts/Reeves etc haven't got ahead of the game and offer both castings and 3D printed parts .....sadly I think the writing is on the wall for expensive casting kits?

[Dave Otto]

Happy they turned printed out OK.

It won't be long until we will be buying "casting kits" as a tree of 3D printed parts or maybe even just a download. That won't please those that spend all their time Fondling Castings

You can see it already with AFV and figure modeling, even RC planes and boats can all be had for the price of a download.

I'm surprised places like Stuarts/Reeves etc haven't got ahead of the game and offer both castings and 3D printed parts .....sadly I think the writing is on the wall for expensive casting kits?

I did a quick check on a model engine casting that we have had done in iron, to see what it would cost to have printed in Aluminum, it was over $500! So maybe for little engines it could be an option but for the larger ones its probably still more cost effective to have castings made.

Dave

[Jasonb]

Stuart do supply some parts CNC cut rather than the old brass stampings. Reeves have been scanning their patterns and also offer a scanning service.

Yes it won't suit every part but by the time you take into account pattern making and fettling the casting costs are not always so high. And a lot easier to find a 3D printing service than a foundry that will do one offs without the usual casting flaws.

[Dave Otto]

Stuart do supply some parts CNC cut rather than the old brass stampings. Reeves have been scanning their patterns and also offer a scanning service.

Yes it won't suit every part but by the time you take into account pattern making and fettling the casting costs are not always so high. And a lot easier to find a 3D printing service than a foundry that will do one offs without the usual casting flaws.

Yes for sure, if I only wanted one for me I would probably just spend the money rather that dealing with all the above mentioned things, which I'm painfully aware of.

Dave