The accessory keeps slipping out. I am trying to use this tool to score the old grout on my bathroom floor. I have never done this before and would like to know what I'm doing wrong. Any info I can get will be appreciated.
Thank you.

I assume you are using a Dremel or something similar. Make sure the bit is fully inserted and the lock is engaged so the motor won't turn while you tighten the chuck using the little wrench; turning clockwise as you are looking at the bit end. Some locks are push buttons that will engage as the chuck is turning. You will feel it when it engages. Some are switches with a little picture of a lock on it.

I hope this helps. If it doesn't, please check out the user manual.

This should have been my first thought rather than my last, but please follow all safety precautions, especially eye protection. High speed tools can and do throw bits of material all over the place at a very high velocity. A dust mask or respirator is also highly recommended. The owner's manual of the tool probably has a couple of pages of safety warnings. They are there for good reason. Please read and follow them.

And it would be a good idea to practice on some scrap material to get familiar with the tool before you tackle the floor. It will be very easy to damage the tile while trying to work on the grouting.

Good luck.

LA
Thank you for your prompt response. Safety was my real concern when the accessory kept slipping. I finally figured out that the wrench was the answer. At first try, I thought the wrench was too big until I discovered the collete nut had grooves and the wrench fit perfectly. I then was able to really tighten the accessory and it doesn't pull out. Thanks again. I will be very careful.

The bits that are sold have diffrent size shafts. They all look the same but the size is diffrent.
If you take off the little nut your trying to tighten to hole the bit in with. you will find a shiney siver thing with slots in it all the way around. Its hole in the center must fit the shaft correctly for the bit you are using. They sell diffrent size "collets" to hold each bit purchased. Check with the local home center or your box of goodies that came with the tool or new bit, and you will most likely find the part you need.
also when removing old grout with this type of method. Be sure to remove everything within the bathroom and cover everything with plastic or drop cloths. You will create a dust storm like no other. Take your time. If you force the bit it will break very easily. Using a rotary tool to remove floor grout will take a fair amount of time.
You may want to try using another method of grout removal. Either a groute saw. Lots of elbow grease, or you can purchase a groute removal tool that goes into a recriprocating saw. that tool is a little hard to find but using power to do the work is the only way to go.

What is the reason for the scoring of the grout in the first place? If your re-grouting you need to remove all the grout. Not just the surface. If the grout is loose and failing. Re-grouting is not going to fix the problem which is floor movement. All the work your going to put into the floor will only fail shortly after you finish the job if that is the case. Provide us with more info and someone here will be glad to assit you in some ideas on how to make your repairs last.