My Pfaff 4872 cover.ock serger will not trim the fabric. Also the stitch plate is raised up and won't remain in place.

Do you mean the Pfaff Coverlock 4872 serger? If so, the manual shows the threading pattern starting with threading the thread guides on page 14 (page 18 of the PDF). Pfaff has the manual on the product support page: http://www.pfaff.com/en-US/Support/3323 . The current link to the manual is: http://www.pfaff.com/SiteMedia/PFAFF/Products/Machines/Support-manuals/coverlock_4872-manual-EN.pdf . Many Pfaff sewing machine manuals are available from the Machine support page: http://www.pfaff.com/en-US/Support-and-Updates/Support . To find this machine, look for the list of Coverlock machines in the alphabetical list then find the specific model.

ManualsLib also has the manual: https://www.manualslib.com/manual/504967/Pfaff-Coverlock-4872.html . If you Google Pfaff coverlock 4872 threading guide video, you can find several videos that may be clearer than the pictures in the manual. Pfaff has the video of threading their overlock machines here: http://www.pfaff.com/mediafiles/threading_guide/index_en.html . (Flash player is required.)

I hope this helps.

Cindy Wells

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Be sure to use brand new needles in the machine (confirm they are the correct needles for the machine) and make sure they are installed facing the correct direction and pushed all the way up before tightened. Start a chain without the fabric, then when it's a couple inches long, raise the presser foot and add the fabric.

Could be your machine has a timing issue and probably requires service.

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It is difficult to tell what exactly is happening with your serger.

First thing--make sure you RAISE the presser foot BEFORE you thread any of the threads. This releases the tension disks so the threads will seat properly. You may need to remove all the threads and rethread from the beginning, making sure you thread each in the proper order. Start out with the thread tensions set at the ideal setting--usually the halfway point between the high & low numbers. From there, you will adjust them to even up the thread tensions.

Are you actually trimming off some of the fabric as it is stitching? If so, you might try increasing the cutting width (moves the cutting edge further toward the right) so that there is more fabric caught within the looper threads. It also appears that the looper tensions may be too loose. Try tightening the upper and lower looper tensions so less of the thread loops don't fall off the fabric's raw edge.

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most Sergers have a blade adjustment that allows you to move the blade closer to the sewing plate as well as further away sounds like yours may be to close to plate. Open the door to the underside of your sewing machine; their should be a round knob at the base of the blade are. Turn the blade until it moves away from the sewing plate. test and see if you have adjusted it enough so as not to cut your stitching off. hope this helps

heres a links for a manual
http://www.sewingpartsonline.com/instruction-manual-pfaff-4872.aspx

or you can try youtube for a video

have you tried changing the needles

is it possible that the needles are in backwards?
it's very possible that the machine is out of time & would have to be taken to a sewing machine repair shop to be retimed

You may not be using the correct presser foot for your machine.

Sewing Machine Feet

You may be using a low shank when your machine needs a high shank.

There is a Yahoo group especially for Pfaff sergers, and most of the list members have 4872 machines. I am not sure if this is the right place to post the link, but here it is anyway:
http://groups.yahoo.com/group/Pfaff_Sergers
You need to join to access information and assistance. It is not a really active group, but I am sure that if you posted a cry for help, you would get a reply very soon.