Accuracy Of Holes

[rcwarship]

I'm new to milling and am starting a fixture project. The fixture will be made of 2 plates, which will rotate on a pin and have 2 stop holes at 35 degrees off center of the flat plate.
With a DRO can one achieve enough accuracy to drill/ream the holes on each of the plates, or would one figure out a way to drill/ream each hole through both pieces at once.
Since a picture's worth a thousand words, there's an attachment of the fixture I'm planning.
Thanks & Best Regards,
Jon

 

[Tony Wells]

Depends on the clearance involved. You're really into jig bore territory, but If you allow a little clearance (which you must anyway, to avoid press fits), you can do what you are asking. A little care in the setup, and it's possible to hit +/- 0.0005 locations.

 

[chips&more]

You did not specify required locating accuracy. Drill and ream is only as close as the drill bit can locate. An end mill instead of a drill bit will give you better true position…Good Luck, Dave.

 

[Dubbie]

You shouldn't ever really plan to have two pins fit exactly in most situations. One pin should be a tight fit and the second allowed to float slightly along the line intersecting both pins. You can buy specially shaped pins to allow this. They are usually called diamond pins.

 

[rcwarship]

Tony, Chips & Dubbie,
Thank you all so much for your responses, I really appreciate it.
Especially that it is "doable"and that a mill would result in a better locating scenario. Woohooooo Diamond Pins, just looked them up & that is the solution to trying to get the holes/pins to line up.
Thanks Fellas!

 

[Boswell]

Gotta love this site. "What did you learn today Boswell?" DIAMOND PINS!

 

[4GSR]

"Diamond Pins", this old fart just learned something new!

 

[Bill C.]

Another approach is to drill and ream the top plate then use a transfer punch to locate the position of the bottom hole. You could always put the two plates together and drill and ream them in one operation.

Good luck with your project

 

[RJSakowski]

You did not specify required locating accuracy. Drill and ream is only as close as the drill bit can locate. An end mill instead of a drill bit will give you better true position…Good Luck, Dave.

When I am working on separate pieces requiring accurate positioning of with the CNC, I spot the holes with a countersink, drill and undersize hole, run a circular pocket routine to the diameter required for reaming and finish with the ream. The circular pocket routine eliminates any backlash considerations and the ream will follow the hole defined by the pocket.

I put a 3 x 4 grid of 3/16 reamed holes on my CNC mill table for mounting a sub plate. When I have work that exceeds the work envelope of the mill, I can shift the sub plate and appropriately redefine my coordinates and continue machining. I have not had any problem with mis-registration for these light press fits.

 

[RJSakowski]

You shouldn't ever really plan to have two pins fit exactly in most situations. One pin should be a tight fit and the second allowed to float slightly along the line intersecting both pins. You can buy specially shaped pins to allow this. They are usually called diamond pins.

We also used one hole as the "origin" and defined the axis orientation with a slightly oblong slot in the direction of the axis in one plate.