Surface plate question

[finsruskw]

Will a cast iron table saw table suffice as a surface plate in a pinch.
I am attempting to square up a 4" piece of drop from a 2 x 4 bar stock on my mill.
Thinking of taping a piece of 220 grit wet/dry paper to it for polishing one surface as flat as possible for a reference point to finish the other 3 sides in the mill.

Would this piece of mat'l be a good candidate for a pair of vee blocks?

 

[macardoso]

Just depends how good the condition of the saw is and what precision you need for the part. For example a 24x24" grade AA surface plate is guaranteed to be flat within 0.000075" over its entire surface. Do you need this level of precision (not that you could sand it that close anyways, nor would you want sandpaper on your $5k surface plate)? Would .001" suffice?

If you're making Vee blocks for precision purposes then they'll need to be hardened and ground. So the mill finish really doesn't matter. If they're just for fun, then do it to whatever level of precision you want. A lot of people use plate glass for lapping since it is pretty darn flat.

 

[finsruskw]

Just depends how good the condition of the saw is and what precision you need for the part. For example a 24x24" grade AA surface plate is guaranteed to be flat within 0.000075" over its entire surface. Do you need this level of precision (not that you could sand it that close anyways, nor would you want sandpaper on your $5k surface plate)? Would .001" suffice?

If you're making Vee blocks for precision purposes then they'll need to be hardened and ground. So the mill finish really doesn't matter. If they're just for fun, then do it to whatever level of precision you want. A lot of people use plate glass for lapping since it is pretty darn flat.

Wow!!
That was quick!!
Thanks for the reply!

Hardened and ground?
Sounds expensive and something I'd have to hire done who knows where.
No exact precision req'd here, just a fun project is all, I can see where some v blocks would come in handy.
The block I started with was a free cut off from the sheared end of a 21 footer.
If nothing else I'll have a good paper weight!!
I have been using the glass/paper method for several years for resurfacing Kohler heads with good results on my Cub Cadets.

 

[macardoso]

Hardened and ground is expensive. If you need nice Vee blocks, buy them - not expensive.

Fun project, just go for it and see how close you can get it. Share picture and experiences with us.

 

[Janderso]

That plate is probably as good as the kitchen counter. Good enough?

 

[f350ca]

I have a surface plate for measuring off but do most of my layout work on a cast iron wing I removed from my cabinet saw to add a sliding table.
The surface plate is no doubt flatter but for layout work the cast iron surface is more than accurate. Laying out marks to center punch you'd be pressed to get beter than 0.005 accuracy and milling to a line probably worse.

Greg

 

[Packard V8]

Hardened and ground V-blocks are only necessary in a production/tool room/QC environment. For hobby shop use, mild steel will function and survive the use to which they'll be put.

jack vines

 

[macardoso]

Huh, I play hockey with mine, but they never seem to last

 

[Mitch Alsup]

If you have a glide plate and a test indicator, you can run the glide plate with indicator over your saw table and see if it is "locally" flat enough.

My guess is that the saw table is "locally" flat to 0.005". If this is "good enough" then you are home free.

 

[mikey]

I am attempting to square up a 4" piece of drop from a 2 x 4 bar stock on my mill.

Unless your piece is very close to your finished dimensions, you do not need to flatten one side to square your part. Try this:

• Pick one face that is relatively flat and put that against the fixed vise jaw. Put a round bar of aluminum or brass against the opposite face, touching the dynamic/moving jaw and lock it down lightly. Get the work piece roughly straight and level and tighten the vise. Now fly cut or mill the top surface flat. This creates your reference or master face.
• Put the master face against the fixed jaw and use the round bar on the opposite side and fly cut/mill the next face. You now have two flat faces that are 90 degrees to each other.
• Flip the piece over so the master face is still against the fixed jaw. Since you have a flat face on the bottom now, you can sit it flat on the bed of the vise or use a parallel. Again, use the rod to clamp and flycut/mill the third face. You now have three faces all 90 degrees to each other and you can put the rod away. Put the master face down against the bed of the vise or on parallels and cut the last face. Now your piece is square except for the ends.
• You now need to square the ends to the faces. You can side mill the ends or stand it up vertically using a square and flycut or end mill it. Then flip the piece and do the other end and you're done.

Even roughly surfaced pieces can be done this way, provided you have enough material to work with.