Our Fall 2015 Sine Plate Project

[ParisDakar]

In the past few years, many of our robot parts have been designed with precise angles. On our milling machine, it is easy to cut, slot, and face parts at 90 degrees, but not so easy to cut a 45, a 60 or an odd degree angle. And a compound angle? Forget it! Our 2014 robot needed the end of one chassis brace cut at 58.455 degrees, while rotated at 32.15 degrees.

Although we've been making do with a plastic protractor and our eyeballs, the proper tool to cut angles on a mill is a sine plate. Sine plates can be purchased at any tooling outlet, however they are not very complicated, so we will fabricate our own. It will be a good exercise for our team to learn and practice our lathe and millwork so that we are prepared to handle whatever the 2016 robot design demands. The finished sine plate will be a valuable addition to our shop tooling and should outlast me.

So I will try to post our progress, designs, challenges, photos and any other good stuff as we work through. Hopefully other teams can benefit from it.

[asid61]

We have a digital protractor that we use for odd things like that, and a vise that can turn. Even if we had a sine plate, I doubt we would ever use it; this year our 1x1 back braces for our elevator needed a 43.2* angle or something, and we just tilted the vise to within 0.1* and milled it right, and it fit on just fine. We had a plate that needed a 44* angle, so we tilted it in the vise and got a reading to within 0.1* with a digital protractor.
That being said, if this is a learning exercise for your veteran machinists it will teach them a whole lot of stuff, and it sounds amazing. I look forward to seeing hoe this goes. I was very impressed with your power-fed rotary table welding this past year.

[ParisDakar]

Since the primary purpose of this project is to learn, we will keep the design simple, and we may not take steps to avoid extra work if it will show students something interesting.

Basic Design: All steel. 6x6x1 inch upper and lower plate halves. 1 in diameter hinge.

Since 1 inch thick steel plate at 6"+ width is not easy to find at small quantities and reasonable prices, we found a deal on a piece of 3x1x36" cold rolled 1018. We cut four 6 inch pieces of this and welded them together to make two 6x6 plates. Students had big fun using the oxy-fuel cutting torch.

First pic is the bevel we put on the plates to prepare them for welding. 30 degrees with a 5/32" land.

Second pic is a finished plate. Stick welded with a 5/32 open root, E6010 root pass, E7016 fill and cap passes.

http://wiki.team1640.com/index.php?t..._IX_Welding#WP

[ParisDakar]

Got the other sine plate halves welded together. Welded them with the MIG this time, multiple passes alternating sides. Had the machine up as hot as it would go with .030" wire. Too much heat is better than not enough.

So we have the upper and lower plates together. They turned out about 6-3/32" by 6 1/8", and quite flat for such heavy weldments. Took off the backer plates with a roughing mill. Then switched to a 6 flute end mill to put a nice finish on one of the sides. Ran out of time.

Need to finish cut all the sides, then we can work on facing the top and bottoms with the flycutter. And the CAD drawings for the hinge assembly need to be finished. Time is flying.

[Big Ideas]

Originally Posted by ParisDakar

Our 2014 robot needed the end of one chassis brace cut at 58.455 degrees, while rotated at 32.15 degrees.

As a welder, I can't believe you are thinking about precision below .1 deg. or even .5deg. If you have a 6" rod that is off in angle by .005deg the end will have shifted by .0005 inches. I would want to redesign any FRC parts that required that much precision.

[asid61]

Originally Posted by Big Ideas

As a welder, I can't believe you are thinking about precision below .1 deg. or even .5deg. If you have a 6" rod that is off in angle by .005deg the end will have shifted by .0005 inches. I would want to redesign any FRC parts that required that much precision.

If precision was the only motivator for this project, I think they would have either bought a sine plate or used some kind of stress-relieved steel, hardened it, and ground it to final dimensions. Realistically it will probably provide very good accuracy compared to no sine plate at all, albeit worse than a professional sine plate.

[ParisDakar]

Well, those oddball angles came out of CAD simply because it let us put a brace between two odd points on the chassis. We really didn't attempt to cut it that precisely. It was kind a joke when those angles came out. I think we left the brace until last and determined we didn't really need it.

But it pointed out that we needed a way to cut angles without disturbing the vise all the time. That was another lesson, that as soon as you get the vise lined back up dead on, somebody needs to cut another angle.

[Sperkowsky]

We don't have a mill but one of these would have came in handy when we were trying to cut a 60° angle in a 1x1 tube.

[Gdeaver]

In a perfect world we would be so well funded that we would just go out and buy all the tooling we need. Reality is that we are at risk of loosing a big major sponsor. If a fixture can be made from a few inexpensive pieces of metal then that's what we have to do. We also need to spend big money on tooling for our cnc lathe. Money money money.
Students are learning allot from this project. Fall is training season.

[ParisDakar]

Here's a pic after a facing cut on the side of one of the plates. Tool is a high speed steel uncoated 1-1/4" 6 flute end mill. Had this tool in the box brand new for who knows how long and never used it, so we gave it a try. Vertical marks are where we were a little inconsistent with the feed rate. If I remember the plate is about .040 over 6" so we have room to experiment with the best feeds and speeds. We were climb milling at about 300 rpm, feeding at most 2" per minute. Well, sometimes 0 ipm, but the operator was learning. No worries though, we'll get it. One of the good things about machine work like this is that no matter what you're trying to do, it's been done so there's plenty of resources and knowledge around.

http://wiki.team1640.com/index.php?t...le:IMG_315.JPG

[asid61]

That finish is not bad at all for steel, especially for a new operator. I wish our new student machinists would feed that consistently!
Have you ever considered investing in a few carbide endmills, like 1/2" and 1/4", for use on steel? I have found that using a 1/2" carbide for steel greatly improves the finish due to the ~4x rpm that I use compared to HSS.
That and a face mill. I can't get enough of that 2000rpm carbide insert face mill finish!
Also, why have you put the part so high in the vise/ stick so much up?

[ParisDakar]

Why did I put the piece so high in the vise? Hmm, that's a good question. It really only needs to be up about 1/8" to clear the weld, eh? I guess laying the parallels flat instead of vertical would be better.

Carbide. Nothing against it. But in our shop the mill is occasionally used by others of highly varying skill levels, resulting often in tools broken, lost, dulled or chipped. In fact I've been using roughing mills for almost all of our work because they stand up better to hard and improper usage.

[ParisDakar]

We got a good bit of work done this week. We decided that it would be better to rough out all sides of the plates first before we do any finish facing. That is, machining off the welds, the backer plates, and torch cut surfaces first.

For this work we used a six flute 1" cobalt roughing mill (actually measures at 0.964) at a little over 400 rpm. Used a feed rate of 4" per minute for a chip thickness of .006". Took off 20 to 60 thou per pass.

For both trimming the ends and cutting the welds, we laid the plates down or stood them straight up so that we could use the power feed on the X-axis, eliminating the manual feed rate issues of last time.

Discovered that the mill appears to cut maybe a thousandth deeper on the left than on the right, in the 6" plate width. Occurred on 2 or 3 of the plate faces, the other 1 or 2 were not as apparent.

Should have been done first, but the mill should be leveled, and the head has to be trammed. The backlash in the lead screws needs to be adjusted, and the vise needs to be reset dead nuts on the table. None of this has ever been done, and I'm torn between involving students or not in these things. I How do you teach an appreciation of precision that can't be seen?

So we've got 2 plates ready to start machining to final dimensions.

http://wiki.team1640.com/index.php?title=Sine_Plate

[magnets]

Originally Posted by ParisDakar

Should have been done first, but the mill should be leveled, and the head has to be trammed. The backlash in the lead screws needs to be adjusted, and the vise needs to be reset dead nuts on the table. None of this has ever been done, and I'm torn between involving students or not in these things. I How do you teach an appreciation of precision that can't be seen?

So we've got 2 plates ready to start machining to final dimensions.

http://wiki.team1640.com/index.php?title=Sine_Plate

Looks like a cool project! A good excercise to get students to appreciate the level of accuracy required is to have them try to make a perfect cube out of poorly cut stock. They will quickly realize that getting everything perfectly square is not as trivial as they might think! Unless the students have had a decent amount of shop experience, the cube will be out of square by enough to be easily measured with calipers.

[Foster]

Originally Posted by ParisDakar

Discovered that the mill appears to cut maybe a thousandth deeper on the left than on the right, in the 6" plate width. Occurred on 2 or 3 of the plate faces, the other 1 or 2 were not as apparent.

Should have been done first, but the mill should be leveled, and the head has to be trammed. The backlash in the lead screws needs to be adjusted, and the vise needs to be reset dead nuts on the table. None of this has ever been done, and I'm torn between involving students or not in these things. I How do you teach an appreciation of precision that can't be seen?

http://wiki.team1640.com/index.php?title=Sine_Plate

Well you can touch, I've met people that can tell the difference of a few thou, by moving a finger.

The other would be to set up a light refraction to let them see the different bands of heights..