Surfacing two sides procedure

[LazyMan]

I know it may sound a like a newbie question but I want to know how you guys approach this.

How would you guys accurately surface both sides of an 8x6x.75 inch piece of aluminum and keep it parallel? I got a 2 inch face mill and 8 inch vise and a set of parallels. I plan to machine the larger surface and then flip the work over and machine the other side to make it parallel. My concern is that because the work piece is not square to began with, there will be problems with the work lifting as the piece is being clamped. Do you guys just pound it with a hammer until the parallels cant move? Do you use hold-down straps?

Whats the best way to do this in production style environment? I know its fairly basic but I just want to know what others are doing.

[wildwestpat]

Hi

Make sure the spindle is adjusted correctly with respect to the table. Errors will show as steps between the passes. Hold the work down to the table of the machine having taken great care to make sure the work piece has no burrs and the table is free from dirt and dings (heaven forbid that you have any dings of course)and both surfaces are clean. Use your hands rather than rags to check. Clamp the work down using the 'T' slots - machine one side - reverse the plate - clean and reclamp - machine second side. Result is that both sides are now parallel. Any inaccuracies are due to the adjustment of the spindle axis to the bed of the machine. You can get fancy and correct the job by placing shimms under the thick end to compensate or re adjust the machine. Make checking the axis of the table to the spindle (tramming) part of your normal checks - particularly important for vertical mills where the last operation may have required an angle to be set.

In a production environment use hold down clamps of the toggle type either manual or air operated. Make a special jig if the edges also require machining. (Large right angle plate might do.) Clamp with toggle clamps or excentric cam blocks. In a production environment keeping the time to remount the work is key and keeping the surfaces clean is where much of the time will go. The vise and the supporting parralels are in my opinion just too akward to keep all the surfaces clean and any bits of dirt or swarf will lead to scrap parts.

Try and avoid thumping the table - a light tap yes! Also try and keep the number of interfaces between the table and the cutter to a minimum to save error being acumulated.

Most machining can be done without vise. The vise should be used to grip work that has parallel faces OR use packing pieces to ensure the work is held securely. My prefference would be to directly clamp to the table when ever possible. Just make sure you don't cut through into the table.

Hope this helps - Regards Pat

[packrat]

If you have a piece that is warped to begin with and you beat it down in the vice till the parallels don't move and take your first skim/leveling cut, when you loosen the vice it will just go back to being warped but thinner.

In a production situation the way I would do it is-

1. Deburr all parts

2. set a number of parts in vice on edge with the 6" side up and down. Tighten vice and put a 'C' clamp on the stack of parts at each end.

3. Take the bare minimum of the top side, just barely clean up. Deburr that edge with file. Leave clamps on.

4. Turn the stack of parts over in the vice, keeping the same flat face against solid vice jaw. (I always cut slips of paper and put them under the part between part and base of vise. like a feeler gage to make sure part is down against vise) Just barely clean up this edge, don't take to size. Take off 'C' clamps and file burr off parts.

5. Now you have square edges. Lay one plate down against parallels,with your squared side against solid vise jaw. Don't hammer down against parallels just push it down as you tighten vice. Clean that side up. Deburr.

6. Flip part over keeping the same edge against solid jaw. Tap this side down on parallels. Take to final thickness.

7. Now you can square your parts to final size.

cary

[LazyMan]

Thanks for the responses. Squaring stock seems to be more annoying and time consuming in metal working than woodworking.