Allowances for Coatings : Machinist or Drafter? 2

[tommo]

I have a question, it is pretty basic - but I would like to know what the consensus of opinion is.

We make a lot of parts, through job-shops that need to be hard coat anodized, which increases the size of the part by 0.015" per surface. People having work plated will also have the same problems.

When making detail drawings for the machined part, should the drawing give finished part dimensions (after anodizing/plating) - or the sizes that the part needs to be machined to, so that after machining the required size is reached?

e.g.
Case in point: 0.750" Bore required for bushing.

1. Should the detail drawing call out a 0.753" Bore, so after anodizing the finished size is 0.750" OR

2. The detail drawing state a 0.750" Bore with a Finish notation for Hard Coat Anodizing - putting the onus on the machinist to make allowance for plating?

It's just a little detail, but makes a big difference to the final assembly!

Thanks for any hints on how to deal with this, or is there a standard convention?

 

[ctopher]

...in a lot of cases, machine shop vendors send the parts out to their vendors for finish. It makes it easier to track for everyone if they are separate dwgs.

Chris
Sr. Mechanical Designer, CAD
SolidWorks 2005 SP0.1

 

[EngJW]

We use multiple drawings and part numbers for the same part. It is a lot of extra work and not easy to understand, but apparently it makes a lot of sense to those who have to keep track of inventory and where a particular part is while it is being made. For example, if a part is made by modifying another part, we have to make a bill of material for it so that the "make from" part gets charged out of inventory. We also have semi-finished and before-coating drawings, even if it is just a dummy drawing with no picture on it. The final, or top level, part has a bill of material listing all of these.

I think much of this was not done years ago, but computer tracking led to it.

 

[Standing]

Chris,
I have a condensed print from Treffers Precision, Inc. in Phoenix, Arizona 602-258-1554. That has a list of processes with the Mil Spec number and thickness and Comments. So I guess I cannot point right to the page number.


Bradley

 

[ctopher]

OK, thanks Bradley. My copy is revision F. I read it again and con not find anything about notes on drawings. There could be a newer version though. thanks

Chris
Sr. Mechanical Designer, CAD
SolidWorks 2005 SP0.1