Not cutting exactly

[foamcarver]

We're trying to make some crosses that need to have 2 different pieces of wood, and the person we are doing them for says that they are 5,000s of an inch off. We were wondering if that's as good as it gets, or if there is something that can be changed with our sb. Any suggestions??

Thanks
Nikki

[mikejohn]

Mark
I believe that, coincidently,this is the same as the published positional accuracy of the Shopbot, 0.005" or .127mm, but others may be able to enlighten you more.

............Mike

[foamcarver]

thanks, is that on the forum somewhere?

Nikki

[mikejohn]

Nikki,
Go here (http://www.shopbottools.com/prtalpha.htm) and click on the yellow Alpha spec button just below the main picture (you may need to scroll down a little to see the button).

....................Mike

[zeykr]

In addition to machine accuracy, how many thousandths under or oversize is your bit. A 1/4 bit is often not exaclty .250 inches in dia.

[stevem]

Nikki, .005" is the thickness of a sheet of paper. The dimentions of a piece of lumber can easily change by that much between the time you place the lumber on the Bot and the time the machine is finished cutting, or, between the time the work leaves your shop and the time it arrives at the customer's, based on the humidity in the air.

If you have a customer who is complaining about .005" tolerance in lumber, you have a customer who is uneducated about lumber, or who doesn't want to pay for the job. You can easily do something about the first problem. The second problem is a little more difficult to deal with.

[watswood]

With solid wood, I'm not so sure you could get better with a $100k machine. Wood has grain that likes to tell the bit where ot go, depending on the bit diameter, it could be much more significant than .005". It also has internal tension that when cut, the tension is released and the wood goes where it wants. Each board/part will react differently.

[foamcarver]

Thanks, I didn't think .005 was alot, he is VERY particular. Thanks again for all your input.

Nikki

[mikejohn]

Nikki
The solution is in four parts.

1). Take a 3 foot length of a good dry piece of hardwood.
2). Dimension it as best you can to 2" x 2" on the Shopbot.
3). Take it to your client.
4). Wack him around the ear with it!

This is, however, only an opinion


................Mike

[drodda]

Around here we usually cut the piece to 4" x 4" to allow for the shrinking in the area of impact. I would go with Mike's suggestion.

By the way Mike I almost spit out my drink while reading your responce. Thanks for the laugh!