Stop block problems again...

[mackmack]

I have a 4 inch piece of 3/4" MDF clamped to my fence for a fence. For some reason I am sometimes getting about a 1/8" deviation from one end to the other of the cut.

I have tried everything and it is beyond me. I've tried holding the piece more firmly, tried not clamping the mdf so tight... I don't know.

Does anyone have any ideas?

[crokett]

Where is the stop block positioned? It needs to be offset back from the blade far enough so that the stock clears the stop block before it hits the blade. So if you are cross cutting 3" wide stock the stop block needs to be set more than 3" off the blade. If you are not doing this you could be be binding the stock on the stop block.

[Stytooner]

The only things I can think of is that the SMT or it's fence aren't set at 90 degrees.
Sometimes guys have written about the SMFence actually moving a tad depending on where the force was applied with your hand.
I personally like to grab it to the right of the locking knob. I just seem to have the best hold down and pushing combo right there.
It may appear that the stock is staying tight against this fence when its actually flexing a little under the force of the cut.
Examine that aspect of your proceedure and it might point you to the cause.

[steve-norrell]

I have been making shaddow boxes for the spouse to give as presents and ran into two problems that may be related to mackmack's. Almost all of the cuts were 45 degree bevels.

First, some of the boards ended up longer or shorter in the middle than on either side. I traced this to boards that were slightly bowed (warped). I had been buying that expensive stuff from Lowes and it looked like I picked up a few bad pieces.

Second, some of the boards were longer on one end than on the other. This was caused a miter fence issue where the little black thingee on the end of the miter fence was either loose or not absolutely flush with the aluminum part of the fence. I was cutting some short boards (8" to 9") and. depending on where I held the board against the fence, the board would "rock", causing a slight movement that resulted in a bad cut. I added a long piece of UHMW piece that extends beyond both black thingees.

Also, I have the miter slot add-on on the left side of the blade and I found that it was slightly lower than the fixed part of the table. This also caused some up and down "rocking". I releveled the miter slot piece.

Hope this helps.

[scorrpio]

Do you account the blade kerf? If waste is between blade and stop block, the cut off amount will be the block-blade distance plus blade thickness.

[LarryG]

I have a 4 inch piece of 3/4" MDF clamped to my fence for a fence.

The wide range of replies you've gotten suggests that we need more information.

Four inch piece of MDF ... 4" wide (tall), or 4" long?

Clamped to WHICH fence ... rip, or SMT?

A 1/8" deviation where, exactly ... from one end of a ripped piece to the other? Or a 1/8" out-of-square difference across the end of a crosscut? Whichever it is, how long or wide is the workpiece?