Mod Your Dremel 300 to Fit the XPR Multisaw

Ok, so I have a dremel 300 series rotary tool and the other day I bought the multisaw attachment and failed to notice that it only could fit the dremel 400 series. I know stupid right?. Since I live in Mexico and bought the attachment in the US, returning it is not an option and to be totally honest, I was kinda pissed off that I'm obligated to buy another rotary tool in order to use the multisaw. Corporate strategy really sucks for consumers.

So in this instructable, btw my very first one. I will explain how to modify your dremel 300 to fit the XPR multisaw attachment and therefore maybe other XPR goodies.

Step 1: Identifiying the Problem at Hand.

So why doesn't the multisaw fit in the dremel 300?? it's the same diameter and everything. It's very simple really, as you can see in the first pic the multisaw has this two little keys that are supposed to fit into the dremel 400 keyways, as shown in the second pic. So our mission is to make this two symmetrical keyways as precise as possible in the dremel 300. I actually eyedball it and it worked out pretty damn good, you can go ahead and make it as close to perfection as you wish.

Next, required hardware...

Step 2: Short Short Requiered Hardware...

I will explain the procedure I took in order to accomplish the mod, but it's really up to you, the things i used were:

1 Torx screwdriver (i used a T10) to open up the dremel 300 - necessary
1 Flat screwdriver (i used a 2 mm wide, i'll explain this one later) - helpful
1 Xacto knife (to mark center reference). - just helpful
1 Extra rotary tool (my dremel predecessor, always got the job done but vibrated as hell) - substitutable but recommended
1 EZ Lock Cut-off wheel (came with my dremel 300 kit, surely you must have one) - necessary if you do have the extra rotary tool.


If you don't have the extra rotary tool, you can still do the mod by hand with the xacto knife. I don't recommend using heat to melt the plastic, it's a really sloppy way to go.

Step 3: Opening the Dremel and a Little of the Multisaw Too

The first thing you have to remove is the housing cap, i forgot the first time...
next there are four torx screws in the underside of the dremel (opposite to the speed selector), remove them. When your over with this step you will probably notice that a little ring comes off as well as a tiny metal cylinder, it's completely normal, this parts correspond to the "Shaft lock button" we will reinstall them after the mod. (figure 1) The power cable can be removed so we can work easily, it's not a problem to reinstall it afterward. (figure 2)

Now you will have to remove the Overthrow nut from the multisaw, this step is to constantly check for precise dimensions between the keys and the keyways we are about to make:

You will notice that the Overthrow nut has two click-on pieces, take your flat screwdriver and pop them out (figure 3). Once popped out, the Overthrow nut will slide off and a threaded cylinder will show, the cylinder can be divided into two half's finally reveling the two keys (figure 4).

Step 4: Cutting the Keyways!!

Sorry but from here on i will only show schematics from the mod since I didn't took pictures.

So we first align one side of the dremel's housing with the multisaw like so (figure 1). I used my xacto knife to make marks where I was supposed to cut out. Remember the key is not really rectangular but a trapezoid.

¿So how deep should you cut?

from the other side of the dremel's housing (the one without the thread) you can see a small lip. That's how deep you should cut out, either way i found that out by cutting until there was no gap between the dremel and the multisaw.(figure 2)

You should end up with a nice keyway in one side by constantly checking your work and always making sure it's aligned properly. (figure 3)

Repeat the same procedure for the other side of the dremel's housing.

Step 5: Tiding Up!

Remove any plastic debris to ensure good motor operation. Ensemble the Dremel and the Overthrow form the multisaw. Mount the multisaw onto the dremel and ensure a good secure fit.

I've used the multisaw a lot with my dremel 300 with no problem at all, but as always i can't ensure yours will work as great as mine, so I cant be held accountable for any boo boo you or your dremel 300 encounters.

I believe that is all. Since this is my first tutorial i must have made a thousand mistakes. Please leave your feedback on ways for me to make better instructables for your enjoyment.

Thank you for your time!