Clamping plate to mill.

[raferguson]

I need to put some slots in a piece of 1/8 inch plate, too large to fit in the vise. I put a piece of plywood under it, and a couple of clamps.

I drilled 3/8" holes to start, and then started moving the table of the mill-drill, taking the full depth as a cut, but the slot came out at an angle, presumably because the plate was moving under the force of milling.

Should I forget taking a full depth pass, and take off 0.010 inch at a time?

Is my clamping inadequate? Do I need four or six clamps? Is the plywood too slippery?

Do you need a photo?

Not sure how to proceed.

Richard

 

[ChazzC]

Photo of your setup would assist in making comments.

 

[Dabbler]

I have used plywood in the past as a sacrificial backing plate, but I prefer that fine particle board (if I'm using carbide).I would drill all the holes you can, and then use wood screws to fasten it to the board. And then as many strap clamps as possible, even putting some in the way, and taking only the one in the way off, and then putting it back.

Your work can never be too secure!

 

[westerner]

Cut all of these with three toe clamps holding the 1/2 inch plate tight to the 1/2 cabinet grade particle board tight to the table.

 

[C-Bag]

I know it flys in the face of conventional wisdom, but I prefer spacer blocks instead of a plate so I can see that I’m not damaging my table. It’s also why when I’m doing long heavy cuts I use a tool holder instead of a regular collet. Big endmills can suck right down into the work and you’ll never be the wiser until you find your cuts are getting deeper even though you have the Z locked. Tool holders have a set screw that engages a pocket on the endmill stopping suckage

On a piece like that .125 plate I’d usually do two cuts. I can take .050 to .070 DOC depending on how sharp my cutter is and the grade of steel plate. I’d use at least 4 step clamps clamping down on where my spacers are.

Obviously this is just my take on the job and not being a trained machinist it’s what I’ve done to keep from making scrap of my mill table and the work. YMMV.

 

[Ecosta777]

For doing thin parts I use melamine or MDF as a sacrifice plate (larger than the part I'm doing), then one of two things to hold it down. Either double sided carpet tape to stick it to the sacrifice plate, or cover both surfaces of the part to be machined and the sacrifice plate with painters tape- then super glue them together.

You'll have to clamp the sacrifice plate down, but you can use a lot of clamps on the edges to make sure it won't move at all.

 

[ChazzC]

For doing thin parts I use melamine or MDF as a sacrifice plate (larger than the part I'm doing), then one of two things to hold it down. Either double sided carpet tape to stick it to the sacrifice plate, or cover both surfaces of the part to be machined and the sacrifice plate with painters tape- then super glue them together.

You'll have to clamp the sacrifice plate down, but you can use a lot of clamps on the edges to make sure it won't move at all.

I also use MDF as a sacrificial support board; recently when milling slots in Lexan swarf shields. It is dimensionally stable, has good compressive strength and in 1/2" & thicker is very flat – within 0.001" over 6" per my surface plate & 0.0005" DTI.

Just remember what the little boy told Hoyt Axton: Don't get it wet!

 

[raferguson]

I had a request to post a photo of the clamping arrangement. There is a piece of wood under the plate, smaller than the plate.

I plan to make a couple more clamps, and try again. I may buy some double sided carpet tape. Is it hard to remove? Will I need solvents to clean off the glue residue?

 

[ChazzC]

I had a request to post a photo of the clamping arrangement. There is a piece of wood under the plate, smaller than the plate.

I plan to make a couple more clamps, and try again. I may buy some double sided carpet tape. Is it hard to remove? Will I need solvents to clean off the glue residue?


View attachment 429436

Thanks for the photo of the setup. A couple of suggestions:

• Drilling a hole at each end of the slot is good; you can also chain drill holes along the length of the slot to take load off of the end mill. Mill the slot in several passes using a 5/16" or 1/4" end mill so that you are only milling one side of the slot at a time.
  
  
• Use a piece of 1/2" or 3/4" MDF (flatter than plywood and gentler on the end mill), larger than the plate.
  
  
• Rather than your shop-made clamps, get a set of step clamps (probably 5/8" for your Mill-Drill):
  
  
  Your clamps will flex & the wooden blocks will crush with any significant clamping pressure.
  
  
• Double-Sided tape (but not carpet tape) or super glue can work, but both surfaces need to be very flat. For your project & setup you're better off with good clamps.
  
  
• From the photo, it looks like the plate is bowed, maybe due to you trying to clamp it tightly onto the under-sized plywood?

Charlie

 

[benmychree]

For the job shown in the picture, I would use steel parallels and the clamps from a regular clamping set, the ones used in the picture are quite wimpy, no wonder the part moved --- those clamping sets are quite reasonably priced and are a must to have at your shop. I use an array of hardened and ground parallels, but soft steel such as key stock will serve as well, especially if some holes are too close to the edge of the parallel and may be damaged by the cutting tool.