Need Help Figuring Out How To Hold This Part!

[SEK_22Hornet]

Ok - very new to CNC milling. Have a 3 axis mill (vertical spindle that moves in the z axis and x and y axis on the table). I have a very small part that I want to make several of (of course! that is what CNC is for, right). It is a small rectangular part with a hole in the end (drilled and tapped, centered) 4 radius corners, and a through pocket (rectangular). I want to make this part using .375 square brass bar, if possible. I am attaching a drawing. I'd like to do this in as few set-ups as possible. Any thoughts or suggestions? Here is a quick drawing of the part with dimensions.

 

[09kevin]

Dan,
If you use 3/8 X 1/2 stock you can make the part in 3 setups. 1) load stock in the vise and face the top of part then machine the part profile and cutout down to say .370 deep (.005 deeper than the part thickness. Make sure you have enough material above the vise jaws so you don't cut the jaws when machining the profile ) (2 turn part over in the vise and face the part to the .365 thickness (3 load part in vise and drill and tap thread.

Kevin

 

[JimDawson]

Put a piece of scrap stock in the vice, drill & tap a 10-24 hole in it. Drill a 0.187 hole in the part in the center of the inside pocket. Bolt the part to the piece in the vice. Now machine the outside profile and the face of all of the parts. You could also do this using a soft fixed jaw for your vice. Make a soft fixed jaw and drill & tap for 10-24. You do already have a G-code file for making soft jaws....right? If not, maybe it's time to create one.

Move over on the scrap piece, and machine a pocket to fit the outside profile, maybe 0.060 - 0.100 deep. This will locate the part. Then make some small hold downs that will clamp the two ends of the part to the fixture. Machine all of the pockets. Another way to do this is to make a set of soft jaws for your vice, and machine pockets into them that will fit the outside profiles of the part, then insert and tighten the vice. You could machine a few pockets into the soft jaws and run a number of parts at a time. I do this all the time, sometimes even for a one-off part.

You can use the same method as above to locate the part to drill & tap the M3 hole.

 

[SEK_22Hornet]

Thanks to both of you for your suggestions - they got my brain working on the problem!. Jim - I think I will use a combination of multiple parts and a jig to hold the parts - what I'm thinking is to cut say five parts at once (that will fit my vice nicely). I will mill out a holding fixture from scrap that will fit inside the inner pocket. I'll make a top half to clamp the parts using a single screw through the pocket. I'll mill the inner pocket for all 5 parts from the .375 square brass. This will be clamped into the fixture to mill the outside profile while holding the fixture in the vice. Same part zero for all operations (except the Z axis). After the first set of parts I will have five top clamps that will each hold one part using a single screw. I'll sketch it out and post the sketch later. The suggestions helped a lot! Thanks again, Dan

 

[chevydyl]

I made some dovetail jaws for profiling, they allow you to really take some meat off while only holding .075 of stock in the jaws. Flip then face off the dovetail. The reason I made them is cause I pulled the same part out of the vise before making my Dove-Grip (tm) jaws. If you had to make a bunch of em just line up the blocks in the jaws with spacers and have a go at it. The hole in the end is an easy one that's been explained already.

 

[Wreck™Wreck]

Question #1, how many?
10,100, 1,000 or 10,000, this makes a very significant difference in the way one may go about making such a part.

 

[John Hasler]

I'd think about doing as many operations as possible on a single long bar before cutting it apart into individual parts.

 

[SEK_22Hornet]

I'll probably make 10 to start with - I've decided to make 5 at a time. This is hobby work for an item that I hope to sell on ebay. Small market (I think) I'll make some for my own use and try to sell some to help cover my own costs. I need to get my idea drawn up and posted - I've pretty much decided on an approach based on Jim's suggestion. I've started writing the programs already.