3D printed throttle linkage - PeachParts Mercedes-Benz Forum

scottmcphee · #1 09-27-2018, 11:53 AM

I know the car doesn't have a throttle, but you know what I mean. I'm talking about the piece of linkage that moves the injector pump rack attached to the accelerator pedal gizmo on my om603

I needed to remove this piece of linkage to get a tool on #3 glow plug that needed replacement. Prying the link off cracked its ball end. 30 years of plastic patiently waiting to do that finally had its chance. It's a gamble each time you pry off linkage ends of this vintage

For reference, this link is 8mm ball joints on each end, and I measured my link to be set at 15.5 cm ball-to-ball (centers).

Luckily I had been designing ball joint linkage for a different purpose using CAD software and a 3D printer I own. So I had a good starting point. I designed a link for the broken one and printed it out. Just fit on my 6" x 6" printer bed when printed on the diagonal of the bed. Two hours later I had a new piece of linkage in my hands! It's a fixed length link whereas the original was an adjustable link, but hadn't been adjusted from its 15.5cm setting for the life of the car as far as I could tell... so nothing missed there. The new link is just one solid piece of plastic with snap clip ball socket ends.

Using PETG plastic filament... this stuff is tough and just flexible enough to make for a strong part that can snap over the balls and come back into shape. This plastic is immune to most common solvents and would remain strong in presence of the fluids found under the hood, even if soaked in diesel. And can withstand the kind of heat found in that area under the hood without softening.

It's a carefully designed ball socket using a diagonally split-cup. The link rod section is stiff enough to act as the pushrod needed to operate the lever it is working on. The forces on this link are always compressional (ball pushing toward the other ball). The springs returning the system to its resting place keeps compression on the rod even when you lift foot off the pedal.

A little bit of lube on each end, and the link is now driving the car. It's good enough to get me up and running again, so I didn't have to scramble ordering a more proper link. And won't any time soon. I think this one will wear just as well as the plastic ends of the original link. We'll check back in another 30 years ! ha !

I'll try to get the link posted up on https://www.thingiverse.com/ just in case you need to print yourself one.

There's a few different linkages in the area that could also be done this way. Maybe I should design some on spec and print out as spares for next time I'm working in the area if another one breaks an end.

sixto · #2 09-27-2018, 05:42 PM

The lower tech solution is to use metal sockets from a 617.

Sixto
98 E320s sedan and wagon
02 C320

scottmcphee · #3 09-27-2018, 09:53 PM

I hear you, but I had no other links on hand from any other car, so I had to think of something else. I got rid of my parts cars a few years ago... doing random grabs of parts and stuffing boxes up until the tow truck arrived to buy them as scrap. Unluckily, I did not grab links ...

Here's how this link appears from a screenshot of the software that prints them:

ykobayashi · #4 09-27-2018, 11:50 PM

That’s cool. Thanks for sharing. What CAD tool do you use to make your 3d model?

t walgamuth · #5 09-28-2018, 06:50 AM

very cool!

scottmcphee · #6 09-28-2018, 01:18 PM

Quote:

Originally Posted by ykobayashi

That’s cool. Thanks for sharing. What CAD tool do you use to make your 3d model?

Here's the whole tool chain used in this process:

AutoDesk Fusion 360, to sketch idea up

AutoDesk Designer, to do CAD model and make stl file

Cura for slicing stl file into gcode ready for printing

Octoprint running on Raspberry Pi driving a Printrbot Simple Metal 3D printer, to print the gcode

You'd sink $5000 into this setup to make one throttle link, not a good return on investment if that's the only thing you're doing it for

But... you'd be able to stamp 'em out for pennies a piece once you got going.

Which reminds me, if you need one of these, I'd be happy to print one out and mail it to you. At today's shipping costs $10 reaches pretty much anywhere around the world, I'd ask you only cover shipping.

ykobayashi · #7 09-29-2018, 09:30 AM

It is shocking how cheap the machines can get as opposed to the sw tool chain. I wanted to get a printer but the cost of solid 3d cad cam scared me off.

I’ve had the same experience with CNC mills. Getting robust CAM takes $$$. Freeware got me started but it is hit and miss.

Diseasel300 · #8 09-29-2018, 12:03 PM

Quote:

Originally Posted by ykobayashi

It is shocking how cheap the machines can get as opposed to the sw tool chain. I wanted to get a printer but the cost of solid 3d cad cam scared me off.

I’ve had the same experience with CNC mills. Getting robust CAM takes $$$. Freeware got me started but it is hit and miss.

Freeware and the like is fine for the DIY home hobbyist, but if you use something for your livelihood, the cost of quality software is only a drop in the bucket compared to rework, downtime, faulty parts, etc caused by iffy software.

In time, the machines and the software to use them will come down enough to make it reasonable for a DIY guy to do their own printing. Remember when laser printers were only for corporations because they were so expensive? Nowadays you can pick up a color one for under $100 that does a better job than those old ones did. Freeware/Open-Source software will catch up in due time too. Remember Linux distros in the late 90s and early 2000s? LOL! Nowdays though they're a competent alternative to Windoze (assuming you don't need a Windoze-specific piece of software).