[jarthel]

as title. Thank you.

jayel

 

[guzzler]

i usually put the sand paper on a piece of glass (held on by some drops of water) and said in a figure 8 pattern while pressing down firmly (move the part, not the sand paper)... the glass ensures it will remain flat...

g

 

[john_jcb]

Well one way is to use a simple device like this to see if your surface is flat:

http://www.hamarlaser.com/systems/L740/index.htm

make sure you get the software that goes with it. The reports are great.

Sanding on a sheet of glass works very well if you are after a pretty flat surface. For most things a good sanding block works well.

 

[guzzler]

how much does that bad cat cost? actually, no, don't answer that:

"If you have to ask, you can't afford it!"

think i'll stick with my piece of glass!

g

 

[aeberbach]

Why do you want it "flat"? I assume you're sanding wood. If it really has to be flat you could buy an engineer's granite block, rub graphite on it and then rub your piece of wood against the surface. The parts that show black need sanding - this is the same way machinists used to create flat surfaces from a reference block, like when making the bed of a lathe.

The sandpaper on glass idea works well but it is easiest when the glass is very thick (glass can bend too) and very large (because when you sand over an edge with a small block it gets rounded over). Even the direction you ruib will create more pressure on the leading edge than the trailing.

Don't forget wood is not very stable. What is flat today might be curved tomorrow depending on the kind of wood, the section of the log the wood is cut from, temperature and humidity.

 

[jarthel]

It's for a metal chassis.

 

[aeberbach]

If you really want to do it like an machinist would then buy the granite block, some blue marker dye and a scraper. Put the blue on the block, place your metal down on it and then scrape away metal where it is blue. Repeat until all the metal shows blue at the same time. But glass is good if you don't need thousandths of an inch accuracy. I've sanded down Celeron chips to try and get better contact with the heatsink on glass.