I place the fabric on the machine, lower the foot and apply pressure to the foot peddle, when the machine begins to sew fabric is pulled down and the lower thread tangles, the machine make a crunching sound. I have replaced the bobbin twice with Brother bobbins and cleaned the bobbin case.

They are adjustable but should be done by a sewing machine technician. Special tools are needed to get the setting right.

If the feed dogs are not pulling the fabric through the machine, check the presser foot pressure adjustment. It tightens the pressure on a spring on the presser foot bar causing the presser foot to apply more or less pressure to the fabric. The pressure adjustment can be located several places but usually around the head of the machine--to the left of the needle or at the very top of the head. Some older machines simply have a screw that is located under the top lid.

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On some machines, you can lighten the amount of pressure the presser foot applies to the fabric. (Some machines do not have this capability.) But, you don't want to adjust the height of the presser foot.

If the fabric is pushing in front of the presser foot as you are sewing, you might want to try using a walking foot, a teflon foot, or a roller foot.

Kenmore 158 13360 Sewing Machine If this is like your machine, the pressure adjustment is the upright pin at the top left side of the machine. The inner pin pushes down (in various degrees), the further it is pushed down, the more pressure the presser foot applies. To release the inner pin, press down on the outer ring of the pin. It will snap back up where you can again push the inner pin down in degrees. BTW, it is a good idea to always release this pressure pin when you store the machine. If not, what happens is, over time the spring that applies the pressure becomes compressed and no longer applies pressure like it should.

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Sewing Machine Pressure Settings for Machine Quilting

Are you talking about presser foot pressure--the amount of pressure the presser foot applies to the fabric and feed dogs?

Some machines have a dial that can raise or lower the pressure.

Some machines have a screw located at the top of the presser foot bar that can be tightened or loosened. (Unfortunately, manufacturers usually did not include this information in the user's manual.)

Even older machines sometimes have a spring-loaded push-button on the top left of the machine. When pushed in, it collapses the spring that applies less or more pressure to the presser foot. The inner button actually applies the pressure in "degrees" which is regulated by how far the button is pushed in. To release this pressure button, press on the outside ring to release the spring. (Incidentally, it is a good practice to release this spring when you are finished sewing. Storing it with the spring compressed may eventually cause the spring to lose its effectiveness.)

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Parts of Sewing Machine Pressure Adjustment

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Sewing Machine Pressure Settings for Machine Quilting

When stitching together a quilt sandwich, it is recommended to use a walking foot on your machine. The walking foot moves the upper fabric in conjunction with the feed dogs. Sometimes, if the quilt sandwich is not too thick, a roller foot can also help but may not be sufficient for a quilt sandwich.
What is Walking Foot Sewing Tips for Beginners
How To Use Walking Foot
How to Use Roller Foot

You may also check the presser foot pressure on your machine. This regulates the amount of pressure the presser foot applies to the fabric and the feed dogs. If the pressure is too strong, it will tend to push the upper layers of fabric, creating a bubble look. If the pressure is too loose, there is not enough pressure for the feed dogs to physically pull entire quilt sandwich under the presser foot.
(The pressure is adjustable depending on the types of fabric and thicknesses being sewn.)
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When you start sewing, make sure the thread is long enough so the machine does not pull the loose end down into the bobbin casing. It is best to drawn both threads (bobbin and top thread) up through the pressure plate before you place the fabric under the pressure foot.

The quilted fabric may be too thick for the walking foot to move along smoothly. Try using a zipper foot which is much slimmer and can get close to the line of stitching.

Several things to try:
Pull thread tails (both bobbin thread and upper thread) straight back and when you lower the presser foot, make sure they are held down straight back. This may or may not be enough to solve the problem, but it is simple to try, and often works. You might want to hold the thread tails while you start sewing.
Use a starter--folded piece of fabric scrap about an inch long--and begin sewing oink middle of starter. Push the fabric you want to see right up to the starter and keep sewing from the starter right onto your project without lifting the presser foot or cutting the thread. When you finish sewing, cut the little piece of thread between the starter and your project.
Before lowering presser foot, use wheel to lower your needle once and then pull up bobbin thread to top surface of your project. Then hold both bobbin and upper thread tails, lower your presser foot, and begin sewing. Release the thread tails after a few stitches.
Hope this helps. Those nasty "thread nests" are a real pain.

attach the sliding foot by clipping off the current one, placing the sliding food onto the needle plate, lining up the clip with the attchment point and lowering the pressure foot down onto it so it clicks in.

Now, does your machine have a little lever device to the left and just behind the pressure foot, have a look for it. If yes, then pull it down, this is the buttonholing trigger and it connects with the sliding foot to trigger the reverse and stitching of the second side.

Program the machine for button holing, this might be pushing in a numbered code, on my 6500 there are five buttonholes and they each have a code that I enter.

Place your fabric test sample under the pressure foot and put the button into the back of the pressure foot, there is a little ratchet device that closes up holding the button firmly to get the right dimensions.

I always do at least 2 test buttonholes using same fabric, usually 2 layers with interfacing between.

Start the buttonholing sequence by pressing on your machines foot control, it should sew backwards away from you down the first side of the buttonhole, and the trigger should connect with a bit on the slide foot triggering the machine to stop, sew the bar tack, and then reverse and sew the otherside and final bar tack.

That's how it goes on my 6500, I hope this applies to your MC10000 too, it should be very similar. Your machine probably has at least 3 or 4 different types of buttonholes it can do. If you don't have a manual for it, it probably is worth sources one as these machines have lots of features to use.

This is the foot that comes down and holds the fabric layers under the needle.

There will be a pressure foot lever to raise and lower the pressure foot at the back of the sewing area, it usually operates vertically, although some makes have a lever that works horizontally.

The pressure foot needs to be lowered BEFORE you start stitching as it activates the top tension and also helps with the stitch formation by holding the fabric firmly as the needle moves up and down.

You can read some general sewing machine info at www.sewing.about.com too.

Oil might help but it sounds like you don't have enough pressure on the foot. You can take the casing off where the light is and there is a screw back there that controls the tension on the pressure foot. It is not meant to be changed by anyone but a professional. I've changed the tension but it wasn't easy. If you are still interested let me know and I will try to explain.