[crudolph]

Hello,

I'm new to the forum and figure I'd make my first post with a question. I'm also new to milling and CNC in general.

So here goes - lets say I have part that I'm milling out of a square piece of stock. I put the stock into my vice, cut the profile that I want and now need to 'part' off the piece from the stock that was used for the work holding (apologies for incorrect terminology). I've done many searches online for 'parting', 'work holding', 'finishing a milled part', etc… I'm undoubtedly using the wrong terms in my search but I'd like to understand the techniques for finishing a part after having milled it. Flipping it over and facing off the bottom seems likely but I'm also wondering if putting the new milled edges in the vice would be potentially damaging.

Any pointers to websites and or proper terminology would be awesome.

Thanks for listening.

- Chris.

[sortafast]

I am a bit of a hack, so take this with a grain of salt. But my approach is to buy the stock as close to the finished size as possible, but 0.125" thicker (I only machine aluminum, steel stuff is one off usually). I usually cut it 0.100" longer than it needs to be then set it up so that the part is 0.050" in from the indicated edges, or centered in the X and Y on the stock. I do my cuts for the bottom or the unseen part of the piece, then flip it over and face off that extra 0.125" then do all the finish machining. To assist with this I make soft jaws. Basically I got some aluminum flat and square bar that I mill the bolt holes for the vise into, then bolt it into the vise and machine out a pocket to hold the part for both the top and bottom ops. This way if I screw up and the endmill eats into the jaws its no big deal. Regular steel vise jaws are hardened and love to kill your bits if you don't watch it. It can be a little tricky at times and requires a lot of thought to get the lay out right, for me at least, but in the end you get repeatability and better clamping. Hope this helps some or gives you some ideas on how to do what you need

[palr717]

You could set the part on parallels and saw it in half with a CNC tool saw? Idk what the right name for the tool is, but yeah. your part would likely come flying off a bit though lol.

[awerby]

"Parting off" usually refers to a lathe operation. Generally milled parts are attached to the block they came out of by small tabs or "bridges" that hold it in place while the milling operations are being done. Afterwards, they can be cut off, either by hand, with a hacksaw, or with the mill, if you've figured out another way to keep it from flying away when it's cut loose. It's hard to talk about your part without seeing it, but yes - holding it directly in the vise can damage it, if you aren't careful about how you do that.

[palr717]

"Parting off" usually refers to a lathe operation. Generally milled parts are attached to the block they came out of by small tabs or "bridges" that hold it in place while the milling operations are being done. Afterwards, they can be cut off, either by hand, with a hacksaw, or with the mill, if you've figured out another way to keep it from flying away when it's cut loose. It's hard to talk about your part without seeing it, but yes - holding it directly in the vise can damage it, if you aren't careful about how you do that.

I think the best thing to do is to make a fixture with a slot wide enough to accommodate a saw. The fixture would hold both the top and the bottom piece so when you cut it the part that you're cutting will stay in place. Simple, fast, no fuss (aka parts flying off the fixture, not having to turn it over and face it off). We used to do this with a part we made at my last job shop.

[louieatienza]

You can -

1 - Use thicker stock, mill the part to depth, then turn the stock over and surface off the remaining stock. If you're afraid of marring the milled edges, you can make aluminum jaws for your vice and mill the negative profile to hold the part.

2 - If the part is rectangular, use a stop on your vice to put in a blank, then after finishing one side, flip it over and set it against the stop (you set the corner of the stop at 0,0 in CAM)

3 - If the part has holes, use a fixture plate, drill or mil the holes first, then bolt through the holes into your fixture plate before you profile,.

4 - Use a vacuum chuck, made specifically for your part if you have to run multiple pieces.

5 - Design "tabs" to hold the part, then use a cut off wheel to free the part and remove the tabs.

6 - Sometimes, you can mill down and leave like 1/32", then switch to a smaller endmill to finish the cut. The piece will drop down, and since you're using a smaller endmill it usually won't jam up.

Basically, there are many ways to do this, and it all depends on the situation; some ways work better for some parts than others.

[zach540]

crudolph,

No expert here, I am just starting myself, but I can tell you I have learned a ton from watching the NYC CNC channel on Youtube, and he has several videos showing the CAD, CAM and machining operations of exactly what you are asking about.

Zach