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Creating Micro-screw from aluminium cast

Hey, I like that chilled idea! At first I was in the PLA FDM material camp, but then I had this idea:

Build an insulated vat to go around the block of material (styrofoam box with no lid), then put dry ice in the vat and submerge the material in isopropanol.

This will get the material very cold (be sure to compensate for thermal growth) and should make it very stiff and easier to machine. The isopropanol may have some lubricating effect on the tool, allowing it to cut without the material becoming gummy and welding to the tool.

I think you might need to 2nd op the hole for the welder, or you will waste material with a keyway type cutter doing the undercut on the chamfer, then use a dovetail tool to cut the chamfer. You can get to the welder hole straight then. I'd probably use a box cutter blade to release the parts from the block after machining, kind of like shoveling snow.
 
The 3D printing idea seems like a good one - except most PLA printers aren't very precise, so wouldn't hold the tolerances.
But ... for only one or two, you could 3D print a 'blank' and then turn it. With precision on the rod basically non-important, you could run it hot enough it would really melt together nicely.

Of course, if this is more than just testing, and you need precise material control for medical device standards, 3D printing might not be the easiest option.
 
Perhaps this link can help you in your endeavor.

Hello All,

I am a researcher at the University of Michigan and I am currently trying to find a way to make a pin that will hold together the structure of a rat jaw bone graft. The pin is very small, a diameter of 1.5mm at its thinnest part and 2.85 mm in length (see attached pdf). The pin also needs to be made out of PLLA (Polylactic Acid) which melts at a very low temperature (50-60 degrees Celsius). The only way I could think of creating this pin is by machining a mold in aluminium and then melting plastic into the mold. Does anyone have any ideas that could make this process easier or have experience trying to make something like this. Thanks for the help!

-DRLOUView attachment 154138

Hi Doc. Please let me know if this will work for you.

XYZprinting da Vinci Junior 1.0 3D Printer B&H # XY3F1J0XUS00 MFR # 3F1J0XUS00C

B&H Photo Video Digital Cameras, Photography, Camcorders
 
How would I machine such a small piece of material? The material itself comes in blocks therefore for me to be able to lathe it I would need to still make some sort of mold and so I could get the plastic into a rod. The engineering technicians in my Mechanical Engineering lab said that I would have a hard time lathing such a small and flexible rod.

Saw the block into square rods somewhat larger in cross section than the largest diameter of your part. Put the material in a 4 jaw chuck and turn it to size. If your shop has square 5C collets, cut it to fit a collet. If it's as flexible as you imply, you may need to support the outboard end on a center. I have no experience with the material of interest, but the low melting temperature does suggest that if you need several of these, it might be easier to make an aluminum mold and just cast them.
 
Hi, you are asking about methods of manufacturing the micro screw from a machinable plastic, not from an aluminum casting right? So the most important parts of this operation are first the accuracy of your lathe, and second the tool sharpness. Diamond tool inserts are nice, but I think a very sharp honed 45 deg. tool steel bit is necessary. Feed and speed should be around 0.001 at 2000 rpm. with a pass for ruffing size and a finish pass to give you final OD. Then cut your speed to thread the smaller dia, 200 rpm, and watch you don't run into the chamfer, and drill. I'd clean in IPA. Good Luck, STuttle
 
Hi Doc. Please let me know if this will work for you.

XYZprinting da Vinci Junior 1.0 3D Printer B&H # XY3F1J0XUS00 MFR # 3F1J0XUS00C

B&H Photo Video Digital Cameras, Photography, Camcorders

100 micron resolution, that's only about 15 units across for his part, definitely not the kind of resolution he needs for a precision part.

The other problem with FDM is that the layers don't fuse to solid like consistency, there is still a grain that is present, which would be detrimental to his intent of proving the material and part will be suitable for jaw bone grafts with ultrasonic welding.

He's using PLA because it's an inert dissolvable material that the body will reclaim and new bone will grow where the PLA rivet was.
 
Try extrusion

Hello All,

I am a researcher at the University of Michigan and I am currently trying to find a way to make a pin that will hold together the structure of a rat jaw bone graft. The pin is very small, a diameter of 1.5mm at its thinnest part and 2.85 mm in length (see attached pdf). The pin also needs to be made out of PLLA (Polylactic Acid) which melts at a very low temperature (50-60 degrees Celsius). The only way I could think of creating this pin is by machining a mold in aluminium and then melting plastic into the mold. Does anyone have any ideas that could make this process easier or have experience trying to make something like this. Thanks for the help!

-DRLOUView attachment 154138

Contact the fibers group of DuPont or whomever owns them and ask if they would extrude you a reel of the stuff and the your lab can cut to length. With that melting point it should easy. You may have to supply the die with a EDM bore to match.
 
I would machine the pin from 3 mm thick PLA plate, starting with the 0.5 mm counter bore on the back of the plate. The part release is done on the flipside. The only feature that would require a lot of creativity is the 45 deg taper on the head. I don't have any 45 degree chamfer mills. There would also be a step near the 1.5 mm pin shaft. So how many do you plan to make?
 
When the 3D printer lays down a 100 micron dot of plastic, wouldn't 15 of those dots laid side by side equal to 1,500 microns (1.5 millimeters) in length?

Yep. That will make for a very rough part and it will have almost no distinguishable features. And that's if you have the process tuned perfectly and get ideal results from the printer.
 
Could you shave or pinch off a piece and then extrude it out of a heated syringe into cold water? You could bore the syringe outlet to the correct diameter or bigger to allow for shrinkage.

You might need to spray a cold mist when machining it.

Sounds like you have a great job.

Cheers
 
Lotta good ideas so far. I would tackle this job with a watchmaker's lathe.
What? Your mechanical engineering lab technicians don't know about watchmaker's (jeweler's) lathes? In this world of ever more tiny structures that offer paths into new mixes of materials and mechanical design principles there is much to be relearned from the antique technology of watch making.
I like the idea of cooling the work with a small stream of inert gas released from a high pressure cylinder. Nozzle size and flow rate can be adjusted to get the right cooling of the plastic to allow machining but not excess brittleness or fouling with ice. If this doesn't work employ a "machinist's box cutter". This is not the common breakaway knife blade. Rather it's a screw machine trick where two tool bits spaced the desired diameter and 180 degrees apart to balance cutting forces. Requires a special tool holder that sorta looks like a follower rest to hold small cutters. Fabricate the whole thing on to a 3/8" or 1/2" shank to fit in any small engine lathe to position two 1/8 or 3/16 square tool bits. Include circular features on the tool holder to enable easy indicating to the lathe centerline as well as setting both tool bits to cut the desired diameter equally. Ed Weldon
 
Don't know why you dragged my name into this thread shit head, but i have not and will never be making parts for any kinda animal based experiments. Its the complete opposite of both mine, my companies and my customers ethos.

You want to experiment on jaw bone implants, if i ever lay hands on teach me, hes going to be kneeing a full on set. I want to make it clear im in no way complicit with any of the animal testing this cunts upto!


Well, way to disprove my point. I was poking fun at lionelt because he missed the very obvious joke of "Why not get a rat that doesn't need a jaw bone graft" with his response of "Well, that's pointless if he's doing animal testing"....


Sheesh, have a cuppa and read it again. :cheers:
 
Hello All,

I am a researcher at the University of Michigan and I am currently trying to find a way to make a pin that will hold together the structure of a rat jaw bone graft. The pin is very small, a diameter of 1.5mm at its thinnest part and 2.85 mm in length (see attached pdf). The pin also needs to be made out of PLLA (Polylactic Acid) which melts at a very low temperature (50-60 degrees Celsius). The only way I could think of creating this pin is by machining a mold in aluminium and then melting plastic into the mold. Does anyone have any ideas that could make this process easier or have experience trying to make something like this. Thanks for the help!

-DRLOUView attachment 154138

This shape has a short elongation factor and could be done on a watchmaker lathe from 3mm filament.
I would use a 3mm collet to clamp the filament and do all on the lathe. Cutting off might leave a very small burr that would need cleaning.
How many do you need?
If you need high quantity, yes, an aluminum mold would be the thing. Would help to have some release angle. How is this part meant to be used ? I mean, does it receive a screw ?
I will take a look at how easy it is to cut on the lathe and let you know...(I have 1.75 PLLA filament and a lathe)
 
This shape has a short elongation factor and could be done on a watchmaker lathe from 3mm filament.
I would use a 3mm collet to clamp the filament and do all on the lathe. Cutting off might leave a very small burr that would need cleaning.
How many do you need?
If you need high quantity, yes, an aluminum mold would be the thing. Would help to have some release angle. How is this part meant to be used ? I mean, does it receive a screw ?
I will take a look at how easy it is to cut on the lathe and let you know...(I have 1.75 PLLA filament and a lathe)

Well, I tried turning PLLA 1.75 mm diameter. This material is very soft.
I was able to take 0.25 mm out to bring the diameter at 1.5mm
However, it is so soft that I couldn't make the pin longer than 1.5mm
Also, the material leaves a bur. See image.
Last, if this needs to be sterilized, tools will have to be prepared accordingly.
Being so soft, it tends to be imprinted with anything that is pressed against it.
Starting with a bigger diameter (3mm) would help.
I think a small mold would be your best solution.
You could actually use a 3D printer to inject into a small mold.
The mold would have to be polished.
What are your tolerances ?
 

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I would machine this on a lathe and use a vortex tube to chill the part while I was cutting it to keep deflection to a minimum. You will need a lot of compressed air to run through the vortex tube though.
 
How about turning it using a liquid nitrogen setup instead of coolant. There a few systems on the market for doing this.

Paul
 








 
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