Post-013
Feb. 1st, 2022

Machining adventures part 3: a gift for shop manager pat.

Everyone has a shop manager in their life, thank them once in a while :)!

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So our Edgerton Center (N51) shop manager Pat — is turning 60 soon and we want to make him a gift that's worthy of all he's done for us. Because we've started learning how to use the HAAS, we think he'd appreciate something CNC'ed out of aluminum or something. Taking a little inspiration from Alex Hattori's gift to Marty Culpepper, we could CNC Pat's name into a block of aluminum.

But for Pat we wanted to add something special to this because he's been at MIT helping students for longer than most of us have been alive. So we kinda wanted something a shop manager could look at and go "aw that's cute" or appreciate that by making a custom version of something that's already a typical thing in the shop. We looked around our shop @ Biomimetics Lab and low and behold, look @ what we found!

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Soft jaws! For a vise for a mill! Not so much for utility purposes but if we CNC his name into something like this he could display it on his desk or at home and it could be this cute, custom engraved shop tool for display! 

The soft jaws we have are 1x2x6 soft jaws but since the holes are always slightly offset from the center line due to the standard design of vise jaws, we went looking for a CAD online as a start/base and indeed we found one — shoutout to Chris Callender on GrabCAD.

The side where the holes are closer to the edge is the bottom of the soft jaw allowing the top to stick up and over the vise to protect the steel from being run into by the end-mill. We will respect this orientation for accuracy. Time to head over to Fusion 360 to edit the CAD from above.

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We started with the Nasalization font and then extrude cut away the face of the soft-jaw. Notice there are two dowel holes in this soft-jaw that are not in our actual soft-jaw. We will remove them later.

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Then we created a "webbing" with fillets we thought would look cool with the rest of the part, and extruded it to the original thickness of the soft jaw. This way we're CNC-ing out the "pockets" of the webbing and the letters themselves. We may need to add some fillets on the letters to get this to work. 

We need a 4mm flat end-mill to CNC this out because of how small the webbing and the spacing between the webbing and the letters are. Let's see what's in the inventory. We actually have a 3mm flat, so that's great.

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Now for the CAM of course. We used a 3mm flat end-mill in tool #6. We used 300SFM and a maximum roughing step-down of 0.3in. We left no stock-to-leave and we're using pocket-clearing as the machining strategy. The machine may try to clear out part of the hole that's in the vise already but it hopefully shouldn't go too far as we set the z-height bottom to be -0.1 inches from the top which is the same height as the depth of the letters.

Now let's setup the HAAS and make sure we fixture everything in the correct direction yea? And darn, while zeroing we broke the end-mill doing the handle jog. Welp, gotta go find another one now. 3mm carbide, 12mm flute length, 38mm overall, 4 flutes, the one we broke was also TiN coated I think. Here's the end-mill we ordered, it will come on Tuesday. We'll continue writing this post then.

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Ok it is now Tuesday — and the end-mill has arrived. We're going to go ahead, re-setup the HAAS, try not to break the bit in setup this time, and export the CAM to a flash-drive. We should also run spindle warmup b/c it's been some time.

  • So spindle warmup first, while I'm updating my supervisor Elijah on other progress.

  • Setup and zero the parts.

  • Run our typical "is the zero-ing correct" test.

  • Export the CAM and run the program and hopefully don't break anything.

Just a quick reminder because I keep forgetting, the order is "list program," "select program," "mem," and then hit cycle-start to get a program running on this machine. Shoutout to McMaster for the above photo's product placement. It's also good to remember the HAAS's units are in inches, especially important when post processing.

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It's always the most heart-stopping moment when you first test rapid and it goes to the zero position. This time it worked and since we only have one tool we don't need to worry too too much. No matter how many times you do it, it doesn't get less stressful, but I guess you don't want it to you want to stay vigilant. 

Here are some obligatory machining videos, you can start to see the pattern and Pat's name coming out in the second one. The machine will take three step-downs according to the CAM to get to the full depth. 

Machining Details:
~300 SFM
10000RPM
~25in/min
FPT 0.000625

A lot of the above came from Fusion 360's in-built machining calculator. That includes the speeds/feeds and FPT. 300SFM was something we selected based on Satchel's previous machining work in the lab testing the smaller end-mill surface finishes so thank you to Satchel for the help in setting our feeds and speeds. 

You can hear some jittering while the machine makes tight turns around the smaller geometry on the part. But overall it's making a pretty good sound and the surface finish looks nice from afar. The machine is on it's third pass so we'll take it out soon and judge it that way. Excited for this one! It'll be a cute gift. We will likely paint or sandblast it for finish/effect. We'll go to shop tonight to see what's lying around. 

Note to self, another thing we have to do at some point is get the coolant working. The aluminum is CNC'ing fine without it but it would be nice to have it to reduce tool wear and improve part surface finish. 

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Ok I re-looked @ the CAM and there's actually 4 total passes. So we'll probably be here for another 10 minutes, but no matter. Take a look at this wonderful picture of the tool-paths. I'm including it here because it's very pretty and for no other real reason.

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Here's the part straight out of the mill. The surface finish is quite smooth and you can see the pattern the end-mill took to clear the material. There are no significant burrs on the surface and honestly these feeds and speeds seem quite solid.

The only small issue I have leaving it like this is that in the places where the end-mill spiraled downwards into the part, we could see the spiraling into the face on the surface of the part which breaks up the smooth lines that form the machining contours. This kinda makes the surface finish less desirable. We could try a finishing pass next time that produces a smoother contour, maybe a ball end-mill would help as well.

Between spray painting (which might have mixed results), anodizing (which would be awesome if we had those capabilities on hand), and sandblasting we chose our typical favorite. 

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Here's the obligatory before and after sand blasting pictures. The sandblasting was done from multiple angles at the top so that the crevices in the "waffle" pattern could be treated as well. The hole was sandblasted by swirling the nozzle again at multiple angles.

Now we want to do some glamor shots, both in the machine shop and under some funky lighting just to spice things up before we give it to Pat tomorrow.

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Here's some fun pictures. We had a spicy purple light in our room that produced a tasty effect on the sandblasted aluminum. We also had a tapped-hole fixture plate to use as a backdrop or other complementary item in some of the photos.

So I think overall this time, we learned to be careful when zero-ing the HAAS so we don't break bits. We learned we need to re-evaluate our machining techniques for surface finish visually (the smoothness was fine). And we CNC'ed a fun pattern for the first time! 

This project was a lot of fun and I super hope Pat likes it as a desk or shelf ornament. He's been an amazing mentor over the years and we hope this small gift is thoughtful enough to convey that.

#machining #patterns #waffle #magenta