Scratch Build – Complete GwassGween -FINISHED-Nov13 2013-pics start on page 67

Thanks for the concern guys, but I said sneezing blood, not coughing. The big monster honker on my face has always been good for picking up dust. I'm not anywhere near sick. I'll leave my mental state up to debate though.

@Monkey - McMaster has 150grit WET sand paper. That would set you up so everything is wet sanded. -I still have a case of dry paper to go through before I can get some.

@Lose - I don't know, man. The hole on that one is kinda big...

@Kayin - Ouch. No more MEK in the house - especially around that chain-smoking cat.

@Waynio - I think the little fan over the toilet is cheaper than buying a hazmat respirator. Paint respirators rule, if you fog your glasses, you don't have it on right. They've saved my bacon while dry cutting tile and sandblasting.

 

Congrats on 1.000 replies!

 

Thanks. Most are me.
-There's another one!

 

Has the garage warmed up yet.

 

Or you could just use a simple face mask like people where when they mow the lawn...

 

Tried them, no good combined with safety glasses & leaning over a work piece for long times, steam up & can't see, could just be cheapo face masks or glasses though & guess it must be if no one else has this problem.

 

Mask.. pffft .. just gargle with old razor blades? Hey, anyone got aspirin and some liquor, head hurts ...*cough *cough ... black stuff coming out of nose and throat..*cough*cough ... don't need no stinking masks ... yes you doyou know better!

 

Gah! Ya keep bumpin' me.
I'm currently getting jacked up on caffeine so I can work out there and not lose a foot.
-Also someone started another sketchup contest.

 

-Here's something similar to the last post, only you might notice I added the top plate. I swear it's not this crooked in real life. -Not sure what happened in the pic.

-Here it is with the lid down. I have since sanded, countersunk, and polished the lid.

-I re-milled the mosfet baseplate. Since the last job was a huge bomb, I decided to work one part at a time.

-The only way to get this stuff free is to cut out a layer of the MDF, and soak that in the sink for an hour.

-The top of the mosfet block started as a 10.7 ounce bar of brass. Here I've milled one edge down, milled one face of the hex down to the base width I need, and flattened two sides so I could clamp it into the vice properly.

-Next I milled out grooves near the base.

-Once I brought the part in to inspect it in some proper lighting, I noticed something was WAY off. It turns out I managed to knock the head of my vise out of true at some point. After fixing that to the best of my ability, (poorly,) I re milled the grooves even.

-I let the CNC take care of the next bit. Here it is shaving off the top of the bar. This is one hour into the process...

-and two hours in. ***! It started to get cold too.

-Here I'm finished for the night. I really hate brass shavings. It cuts beautifully, but leaves chips like razor-sharp needles. It burns like hell if you get them in your skin, too.

-Here's where I'm at with the project. Judging by the tilted cuts on the face, I'd say I need to level my cutting axis too. Someone must have used it as a leaning post at some point.

-I'm leaving the big flat spot in the middle there for a while. It should be handy for centering and leveling. The current weight is just under 4 ounces.

Thanks again for reading, and thanks again to my sponsors:

 

Goooooooooooooooolllld!!!!!!!!!!!!!!!!!!

 

Not yellow enough.

I got another stumper for the machinists here: Somehow I managed to get the bottom cut 'bowed'. The edge I milled down to be the base is higher on the edges for some reason. I can't figure out what happened. I would think even if the Z axis was tilted and the head of the vise was crooked, it would still cut a straight line along the X axis, right?

It's bizarre because all the other flat milled areas are dead level. It's just that first cut that was screwy.

 

You'd have to point in a picture to where you are talking about specifically...but when you don't have a consistent angle along the part, even if it is not a 0° angle, that makes me think it was a clamping issue. If the clamping pressure is too high, the part could bow. It is a rather thick piece, but brass is soft (copper!).

 

Well it looks nice. From that last photo is the center section .020" low?

Must be a clamping issue as Achron said. Do you have a dial indicator?

 

@Craig - No, I don't have any calibration gear. just a square.

-Here's a quick pic. You can kinda see the bottom is not touching the table in the middle. The top is dead flat. As this was face milled you would think it would have cut flat like the top. I don't think the material could be bent this easy, and there's no way a 2" clamp could do it.
I kinda want to know what happened so it won't happen again.


-On a side note, I milled the water channel out last night. As exciting as that is, don't follow the newspaper ad's instructions.

Edit@Craig - The thin table area does have a bow to the bottom now that you mention it. That bit was crooked, then I re-squared the vise and cut them again. Even crooked, the mill should have cut a straight line, right? I feel like I'm defying the laws of physics here.

 

Glad to know my eyes work

What I would do is remove the vise and clean, clean. then can the bit go to table, if not use a flat spacer, so bit just touches move table so you can check it runs true, adjust as needed and square head to table. Replace vise and check bit height on vice corners. Hopefully all the same.
Then put piece base up align corner heights and re-mill to center depth.

 

Nice milling but unfortunate with the bowing.

I can think of two ways this could happen, First one is the same reason that achron is talking about. The clamping force create an internal tension in the material making the piece bow slightly. When you release it after you have milled it flat, it bows back and the flat surface becomes bendt.

The second one could be that there is internal tension/stress in the material from the start. If the material isn't stress relieved before machining (I have no clue how to do that), these internal tension can make the part deform after you have removed some material. The more material you remove the more apparent this internal tension becomes and the bigger the bow is.

I had the same issue with my HD holders. I made a total of 3 pieces looking like the ones in the drawing below. Two of them turned out as the top sketch and one like the bottom one. None of them were perfectly flat even though I used a really good vise with paralell blocks and hamered it down to be in perfect position.



I would probably blame your distortion problem on my last guess, the internal stress from the material in the beginning since it looks like you remowed quite a lot of material on the top.

An other example is when I ordered a prototype heatsink at work. It was machined with a EDM machine, a process that doesn't need a lot of clamping force since there are no cutting forces. The base of the heatsink still turned out crookid because of the big amount of material removed from the top and the internal tensions. I managed to save it by facemilling it though.

The thing I would try In your case is to reduce the clamping force and maybe take very shallow cutts and then reclamp the piece and take another shallow cut and repeat. Maybe try to rotate it 90 deg in the vise mill it in a different pattern.

Good luck and I hope you get it sorted out because it looks really good.

 

To counter what GNU said, I would take off smaller passes and flip the part more readily. This removes the stresses and evens out the piece more than if you took a single large cut on both sides.

 

One way is to remove the same amount of material on both sides, to even out the stress.

Brass IS one of the worst materials I've worked with, regarding stress.

As soon as you open up the material by milling it, it will stretch/bend. Doesn't matter if it's 0.1mm or 3 mm's you remove.

Another thing to do (That we always do) is to heat it up to red-hot, and mill it roughly to the dimensions you want. Keep 0.5-1 mm. Then heat it up to red-hot again, and mill the rest. In my experience this is the best way to keep something as straight as possible. Maybe even do a last heating and take the last 0.2 mm off.

Just make sure you allow it to cool down slowly, to prevent as much stressas possible from being re-created.

 

THANKS!
So next time I do brass I should anneal the crud out of it.

 

Anneal... THAT's the word I was looking for!

I consider myself somewhat good at using the english language. But when it comes to the technical words that has to do with machining, I'm completely lost!

But yes. The more the better! Before and midways, and even a third run is a good idea. But I would still be hesitant to promise a dead exact straight piece. But lapping with sandpaper should take care of the very last. If you anneal, you should be able to go below 0.001 inch in accuracy.

Just be happy you didn't mill it from a flat bar, that would have been even worse!