Our Fall 2015 Sine Plate Project

[ParisDakar]

Yep, cube sounds like a good exercise. And I'd like to get an idea of just how out of whack this mill is.

[asid61]

I've had to learn to tram the head and such. A few good ways to demonstrate the importance come to mind:
1. Hole sizes. A hole that is 0.001" oversize is vastly difference than 0.001" undersized for bearings and such
2. Squareness. Even a 0.002" off-square block can be seen with a trued square.
3. Gear spacing (?). It's possible to demonstrate it this way.
4. Hole spacing, for dowel pins.

[ParisDakar]

Well actually, you can see and feel the 1 or 2 thou difference, even the students could.

I guess what I meant by 'appreciation' was for the 8 hours of work required to remove that error. An appreciation of not just what the mill is, but what it can make. An appreciation of craftsmanship. Things that are slowly being lost.

[ParisDakar]

Before we did any finish cuts, we decided it was time to check the mill out to see how it was set up, correct anything detrimental to accuracy and give it a clean up.

Vise was taken off, and disassembled. Cleaned out all the piles of chips and dried up oil. Same for the mill table, it was loaded with goo and metal. Cleaned the ways. Checked for dings and divots, didn't find any.

I have to give the student credit who tackled this job, it was quite a mess. We will have to make some rules from now on that clean up at the end of the day will be mandatory.

Put an indicator on the spindle and checked for runout. It read a needle-width maybe .0002, and no noticeable play. Good I'd say for not having any spindle lube for several years before I got there. We were just getting to mounting an indicator to tram the table and ran out of time.

http://wiki.team1640.com/index.php?t...l_151104-3.jpg

[asid61]

Given how you're measuring that, the 0.0002" could just be the rod and the collet, not necessarily the spindle. What's wrong with just putting the indicator tip right in the spindle?

[ParisDakar]

Actually we did. The pic was taken later. We started with the spindle, then moved down and measured a collet, then down to a drill chuck.

I wanted to put the indicator rod mount in a drill chuck, but discovered it wobbled on rotation, you could see it easily. So we traced it back up. The drill chuck was out by .008". The R8/morse taper chuck adapter was good, as straight as the spindle. So we knocked off the chuck and found that the morse taper that the chuck was mounted on was all torn up. No wonder we could never drill a clean hole with that chuck.

In the pic, we put the indicator rod mount in a collet (which was a bit too small) just to see how straight that combination was.

[ParisDakar]

We're still working on this. This week, got one plate finish cut to exactly 6.000" in one direction. Figuring out a good hole pattern to put on the top plate requires some thinking. As does the hinge part sizes and fasteners. I'm stretched pretty thin between designing it, supervising the millwork, and teaching the new team to weld.

[akoscielski3]

This looks like your students had fun with this challenge, good on them. It really seems like a cool project.

I really just wanted to show another way I was used to getting angles on a mill. When I was working on a mill I used "Angle Blocks", Which is a set of precision gauge angle blocks. You can add angles together, and subtract angles. Here is a link to a picture of them.

[ParisDakar]

Tonight we cut one plate to final dimensions of 6.000" by 6.000". After that we used a flycutter to face one side.

Final face cut

[asid61]

Originally Posted by ParisDakar

Tonight we cut one plate to final dimensions of 6.000" by 6.000". After that we used a flycutter to face one side.

Final face cut

Mmmmm flycutter finish...

[ParisDakar]

This week we faced the other side of the plate with the flycutter. Set the tool to cut about a 3.5" diameter circle, so we could face the full 6" plate width in two passes. We cut .003 to .004" with each pass. Only took 3 cuts or about .010" to completely surface this side. 1250 rpm produced the best finish. The cutting tool is carbide tipped HSS. I ground a radius on the point of the tool this week, maybe 3/32". Finish is better than last time when it had a sharper point. Tool rake angle is 0. Feed rate was about 3" per minute for a chip load of a little more than .002".

The mill is definitely out of alignment a bit. When I upload the pics, you can see the difference between a L to R pass and a R to L pass. The tool cuts lower on the left. So on the the L to R pass, the trailing edge of the tool drags the surface producing a fine, sandy texture. Best cut in this case is in the R to L direction, where only the leading edge is cutting.

[ParisDakar]

Originally Posted by ParisDakar

This week we faced the other side of the plate with the flycutter. Set the tool to cut about a 3.5" diameter circle, so we could face the full 6" plate width in two passes. We cut .003 to .004" with each pass. Only took 3 cuts or about .010" to completely surface this side. 1250 rpm produced the best finish. The cutting tool is carbide tipped HSS. I ground a radius on the point of the tool this week, maybe 3/32". Finish is better than last time when it had a sharper point. Tool rake angle is 0. Feed rate was about 3" per minute for a chip load of a little more than .002".

The mill is definitely out of alignment a bit. When I upload the pics, you can see the difference between a L to R pass and a R to L pass. The tool cuts lower on the left. So on the the L to R pass, the trailing edge of the tool drags the surface producing a fine, sandy texture. Best cut in this case is in the R to L direction, where only the leading edge is cutting.

Two shots of the finished plate. Right/upper side is the rough pass.
http://wiki.team1640.com/index.php?t...1209152104.jpg
http://wiki.team1640.com/index.php?t...209152104a.jpg

[ParisDakar]

Making some progress. Milled the groove in the lower plate that accepts the hinge. The tool is a cobalt 1" diameter, 6 flute, center cutting ball end mill. Best speed was about 1250 rpm and a 30" per minute feed rate. A little higher than I expected, but below those speeds, it chattered quite a bit and the finish wasn't that great. The tool really wanted to cut. We took out from .035" for the initial passes to .010" for the final pass.

The final groove depth was 0.156 or 5/32". I had students do some calculations to figure out what was the best depth to give the hinge the most rigidity without being too deep and limiting space between the plates, or limiting the angle to which it can be opened. Calcs showed rigidity increases significantly up to .150", then only marginally past that. Here's the description of the problem I handed out, in case anyone wants to run some numbers. I'd be interested in what you come up with.

http://wiki.team1640.com/images/8/82...te_Problem.pdf

Also put two 1/2" holes in the plate that match the slot spacing in the mill table so we can bolt it down directly if we need to.


http://wiki.team1640.com/index.php?t...1_151216-1.jpg
http://wiki.team1640.com/index.php?t...1_151216-6.jpg

[asid61]

I would be interested in seeing how that was calculated, given the wide range of uses for a sine plate.
Have you checked how flat the plate is with an indicator? I know that when we try doing cuts on the face of a plate it tends to bend due to stresses being relieved.

[ParisDakar]

I haven't checked the plates for flatness. But I'll do that when we get a minute and let you know.

As for the calculations, my best guess was that the horizontal milling forces acting on the hinge would be similar to pushing a car over a curb. If the wheels have x amount of weight on them, how hard do you have to push horizontally to get the wheels to climb the curb. The height of the curb would equate to the depth of the groove.

Of course the hinge won't roll like a wheel. And the milling forces don't produce a straight push on the hinge, it's more of a horizontal torque. So my model isn't an exact approximation.