precision question

[dstacey]

Hay Guys,

I have a precision question for you, I have some 4" square parts to work on so I drew a 4" square box in partworks 1.1 and built a profile tool path to cut out the inside of a hold down piece.

My question is: will the 4" part fit inside the cutout or will I need to use the allowance offset feature and cut the opening in the hold down piece just slight larger?

I have also noticed that the pocket tool path doesn't have an offset feature, is there a way around this?

Thanks,
Dave

[adrianm]

You should upgrade. There have been a LOT of improvements since 1.1

A 4" piece won't fit into a 4" hole without some sort of allowance. The amount varies depending on the material, tool and machine.

[dlcw]

Dave,

The 4" pocket you cut out to hold your other parts is going to have rounded corners, not square corners (unless of course your part to be held also has rounded corners).

The bit diameter will have a big impact on the fit. If you measure your bit to .001" then things will be pretty precise. If you measure to .01" then you could have a looser fit or no fit at all.

Machine flex will determine your accuracy. My PRSAlpha gives me an accuracy (sometimes - when it's having a good day) of around .001". Like Adrian says, this is going to be a VERY tight fit and won't work.

If you are using a wood product for the 'jig' it will change shape and size as the cutting is done and pressure is released from the wood. MDF makes a better material for this type of work but you still have the rounded corner issue along with bit diameter issues.

An alternative to trying to get a super tight fit is to use shims. Cut the holding jig a little oversize and then use some shims to wedge the part in place firmly for cutting. This will also help with the rounded corners issue.

If I was going to be doing a lot of these parts, I would build a jig that had an opening big enough that I could use a pressure plate that would be mounted on a bolt that could be screwed in to wedge the part in to place.

[steve_g]

A slight pocket (.060), an inside corner with the IS corner relieved with a dog bone fillet and shop made cams pivoting on deck screws works well for machining of repeat blank sizes... be careful of anything made with MDF. It'll change size on you!

SG

[bob_dodd]

Dave
A way around it would be ; in the 4 corners to make a drilling tool path to solve the rounded corners , if your software does not have an off set option , edit the size of the tool dia. by a coulple of thousands +/- as needed to make clearance

[dstacey]

Thank you so much.
I figured I would need to add some clearance, but I wasnt sure how tight of a line I should expect. I espically appreicate the pictures, those are some great ideas.

Also, if it's time for me to upgrade partworks, can you tell what that process is and what they charge for the upgrade?

Dave

[oddcoach]

you can also make precise adjustments to the pocket by adding a profile path to the same vector then you have the offset function. To upgrade call Shopbot and talk to Diane. you will not be dissapointed