Line Boring Metal 3D Print

[50BMG DUDE]

Novaguy - I almost hate to ask, but would you PM me your source for the DMLS? I have some parts I'd like to have made but cannot justify having done onshore. They are purely cosmetic and require no machining (other that a couple belt grinder hits) - I've looked at doing them as lost wax or lost PLA and they are not even cost effective then.

Thanks

 

[Rob F.]

To figure out how to mount your piston to the lathe carriage I would get a piece of round stock that fits in the raw pin bore holes, and chuck it up in the lathe chuck with the piston on it and then move the carriage under it to see clearances, compound on or off etc. Wood dowel would even work for that, it may show something not thought of, for good or bad...

 

[john.k]

Firstly,Is the pin hole offset ?...many are.....Secondly. Is the pin hole round ? Many are not,having clearance at the sides ,none top and bottom...........boring the pin hole on a small table fixed to a faceplate is the simplest way to get an accurate result...............I bored Honda car pistons like this,using a sliding bar and a spindle bushing to centre the bore when setting up.

 

[Novaguy]

Novaguy - I almost hate to ask, but would you PM me your source for the DMLS? I have some parts I'd like to have made but cannot justify having done onshore. They are purely cosmetic and require no machining (other that a couple belt grinder hits) - I've looked at doing them as lost wax or lost PLA and they are not even cost effective then.

Thanks

Sent. Prepare to be blown away how cheap they are. I could see if US DMLS suppliers were double the price, but 10 times? I don't see how they can justify that.

 

[Novaguy]

To figure out how to mount your piston to the lathe carriage I would get a piece of round stock that fits in the raw pin bore holes, and chuck it up in the lathe chuck with the piston on it and then move the carriage under it to see clearances, compound on or off etc. Wood dowel would even work for that, it may show something not thought of, for good or bad...

Thanks for the tip! I could just machine the stock until it just barely fits through both bores

Firstly,Is the pin hole offset ?...many are.....Secondly. Is the pin hole round ? Many are not,having clearance at the sides ,none top and bottom...........boring the pin hole on a small table fixed to a faceplate is the simplest way to get an accurate result...............I bored Honda car pistons like this,using a sliding bar and a spindle bushing to centre the bore when setting up.

The pin bore is offset 1mm towards the thrust side. Not sure whether they have that pin bore shape, I imagine it must be a modern piston evolution. These are 1970's Honda XR75 pistons, but it's a good point.

@john.k You have any pics or more info on this setup? Was the table horizontal and bolted to an adaptor on the faceplate?

Here's another way of doing it if I had a Bridgeport:

 

[implmex]

Hi again Novaguy:
I watched the video you linked to in your last post...yeah, the basic strategy this guy uses is sound, but jeez is this guy ever rough with his tools.
I cringe every time he bangs what used to be precision surfaces around...whether he's beating the shit out of the piston by slapping it accidentally with the wrench, or tossing his collets on the mill table, he's not improving the quality of anything in his shop, including his workpiece.
When he whacks the boring tool into the piston at 4:43 and rattles the piston around in the chuck while he's setting it up, I see a guy who takes little care to keep his stuff pristine.

So yeah, a good basic strategy but don't imitate him too closely or you'll be wondering why your stuff never quite works as good as it could if there weren't little dings pounded into it all over.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[Novaguy]

@implmex yeah I agree, he's a bit reckless with precision equipment (and the aluminum piston), but he was a pretty old school guy. I'm a lot less nonchalant when it comes to my stuff...

 

[Novaguy]

Then you have guys like this who have never wound back their torque wrenches (or used them ) but make pistons that must last long enough to keep customers...I respect them for making due with the bare minimum:

Not to make this a YouTube thread, but in my "research" I've come across a lot of methods of piston manufacturing, thought it was interesting and worth sharing.

 

[implmex]

Hi again Novaguy:
Yeah, I've looked at quite a few of these "Git er done" videos from Pakistan and other developing countries, and like you I find it a sobering reality check on just what you can accomplish with some ingenuity, no safety standards and a "good enough" mentality
.

Of course you and I would be horrified to have to work this way, and I'm sure these pistons do not go into high performance engines, but the fact that they are good enough to make the wheels go 'round makes it much harder to assert "but it'll NEVER work".

There's all kinds of things these pistons are not...but hopeless is only one of them if you need the performance that comes with sophisticated engineering and manufacture.

So thanks for the video link...I enjoyed watching it.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[swarfless]

OK if I were faced with this problem piston I'd first wrap shim around it to extend its length, holding shim tube with a hose clip. Fill the cup so formed with one of the low melting point Cerro metals, preferably one that expands slightly on solidifying. Having done that proceed to machine, starting with a now convenient-to-hold chunk of metal.

 

[john.k]

To machine any rough item(cast /forged /printed) you must first produce a register/first cut .......if this is not correct,some part of the machining will not clean up........Incidentally,there is an Australian Piston maker who uses a camelback drill to ream pin holes .........might add the rest of the piston is notorious crap too,but people pay $400 each for them where nothing else is available.

 

[Novaguy]

OK if I were faced with this problem piston I'd first wrap shim around it to extend its length, holding shim tube with a hose clip. Fill the cup so formed with one of the low melting point Cerro metals, preferably one that expands slightly on solidifying. Having done that proceed to machine, starting with a now convenient-to-hold chunk of metal.

Only problem with that is the pockets for the valves would now be filled up. Not something I could easily re-cut, but there is some porosity there which your idea might help!

The piston crown is the beginning of the print and built vertically from there:

To machine any rough item(cast /forged /printed) you must first produce a register/first cut .......if this is not correct,some part of the machining will not clean up........Incidentally,there is an Australian Piston maker who uses a camelback drill to ream pin holes .........might add the rest of the piston is notorious crap too,but people pay $400 each for them where nothing else is available.

Exactly. I planned to cut the bottom of the skirts to serve as a register for the next fixture. Described my original plan a few posts back showing it.

At least the guys with the Camelback drill are reaming in style!

 

[eKretz]

I would imagine that if it lasts long enough for the youtube video it will be golden. Should have had them add a register at the crown of the piston as mentioned earlier by Marcus? Was it? Gotta think ahead sometimes. You could also grip on the skirt first, face the crown, turn the smaller round portion near the ring grooves, then flip around and grip on the fresh turned diameter to finish the rest of the skirt and barrel. Then bore and ream the pin hole with the piston setting on the compound.

 

[swarfless]

Hi Novaguy, I think you missed my point. The Cerro metals are a range of LOW melting point alloys, some melt in hot water. The point of filling your piston with such was to form a solid cylinder that you could machine conveniently, effectively converting the piston temporarily to a solid skirt job & much easier to handle. Choose the Cerro alloy for slight expansion on solidification & strength/machinability, you don't want one like beeswax. The valve pockets would not be filled(wouldn't matter if they were), I meant invert the piston with its shim wrapping & fill it like a cup. Do your external machining & any internal, the cross boring/reaming for the gudgeon pin (I'd either do that, as I have done, clamping the piston on an angle plate on a faceplate, or as others suggested, on your cross slide/boring table if your lathe has suitable). Melt out the Cerro metal when completed. I HAVE used the Cerro metal filling technique on a much smaller job, about 50 years ago, stereo cartridge shell, rounded coffin shape, how to hold? Milled out the inside shape while a rectangular block of aluminium, filled it with Cerro metal (forget the precise alloy), I think I used some drilled holes in the skin-to-be to key, milled the top of that flat, drilled & tapped for a couple of screws to clamp the lump to an ally plate, milled the outside shape to give a 1mm skin thickness, drilled lightening & fixing holes, melt out the Cerro metal, & PRESTO! One dampener .. the Cerro metal would cost you probably more than your piston but is indefinitely recyclable (save the swarf).

 

[Novaguy]

I would imagine that if it lasts long enough for the youtube video it will be golden. Should have had them add a register at the crown of the piston as mentioned earlier by Marcus? Was it? Gotta think ahead sometimes. You could also grip on the skirt first, face the crown, turn the smaller round portion near the ring grooves, then flip around and grip on the fresh turned diameter to finish the rest of the skirt and barrel. Then bore and ream the pin hole with the piston setting on the compound.

I considered adding a shaft to the top of the piston crown - like I mentioned before, that wouldn't required most of the piston to be printed on "support" material. This is the breakaway material that supports any over hangs. You can see the support material below on the Porsche/Mahle pistons inside the wrist pin:



In my experience, anything printed on to support material is lower quality in texture and also dimensions - and this is usually translated to each print layer afterwards. Probably why Porsche prints directly onto the build plate...

@swarfless I understood that, but I didn't realize they were THAT low of a melting point. I figured it would all still have to be machined away. But if you can just apply a heat gun to it and melt it, that's definitely doable

 

[Novaguy]

Considering this project now that I've printed it, I could've probably designed the part WITH an elliptical OD and tapered skirt - then just Skim the OD where it would only clean up the thrust surfaces. And leave the wrist pin holes SOLID, but with a center punch on the outside edge to help locate center.

 

[Rob F.]

What you could also do is a hybrid of both methods discussed. First drill the minimum clean up size to get a round hole through the pin bores and then machine as you originally planned, using the smaller pin to set it up square. After the rest of the piston is machined then set it back on the compound (or angle block on a faceplate) and bore the hole to exact size. This lets you reference the machined surfaces for final hole location.

 

[john.k]

Does the piston need to be oval ground?..........anyhoo,where I start is the ring area ,make this cylindrical and you have a good register that can be used in a simple fixture for all the remaining work........the area above the pin doesnt need to be oval , heat transfer through the pin bearing bosses causes the piston to distort ......back in the day ,cheap car pistons had cast in invar struts to limit expansion.(Repco GM or Ford pistons were $4 with rings and pin.)........other pistons had the head isolated from the thrust faces ,and split skirts ........just because its a slipper piston,doesnt mean it wont seize on the thrust face edges.

 

[Novaguy]

....just because its a slipper piston,doesnt mean it wont seize on the thrust face edges.

That's the one area where I would consider sanding down to match the OEM Honda piston ellipse shape.

But it's very miniscule on the factory piston - 47.95 mm Dia at the thrust faces and 47.73 mm Dia 90 degrees to that, but at the same distance from the skirt bottom. There's also the fact that this 10% silicone DMLS piston may expand more due to geometry and composition.

 

[Novaguy]

Just took some test cuts on another DMLS print from the same alloy (AlSi10Mg).

Left a really gritty finish - best results were from high spindle speed and slowly feeding by hand. The one face cleaned up much better than the rest?

Tried carbide inserts with a radius and HSS tools and they both cut similarly. Worst Al I've ever cut. There is a T6 heat treatment for this alloy and it's low enough temps for a home oven if IRC