Cutting zero clearance throat plate (ZCTP)

[LCHIEN]

I was machining zero clearance plates for my BT3000 and wanted to cut the slot by installing the ZCTP and raising the spinning blade into it. The warning being that if the plate is screwed down and the blade trapped you can break your belts when starting the saw.

So there has to be clearance between the top of the blade at its lowest position and the bottom of the plate, and/or a relief cut in the plate if the pate is thick.

The plastic ZCTP blanks form Ryobi are 1/2 inch thick and have an arched relief in the blade area. I was using a 1/2" thick piece of flooring.
I measured the blade clearance top tip blade fully lowered, to the top of the table

and I could get a 3/16" setup bar with clearance but a 1/4" setup bar touched both sides so at least 3/16".
I put in a relief of 0.25 deep, but I think I'm going to have to increase it to .375 leaving only 1/8th inch at the apex.



Also, the three hole pattern for mounting the ZCTP puts the hole in the thinnest part, very close to the edge, you can see on my plastic ZCTP where it has broken out. I decided to use the four hole pattern which is thicker area farther from the edge.

[SpinDoctor53]

I have a bunch of blanks just sitting for making new ZCTP's. The blank are 19mm Jatoba. AKA Brazilian Cherry (1). What held them up getting finished was I lost access to a milling machine at work. One thing I think I would do is cut a slot and pocket on the top surface so that the sacrificial part is made from 1/4 Masonite. Have master made up and profile the new blanks with a router.

[LCHIEN]

Here's some post experience notes

I cut the blanks, then routed the edge and end rabbets with the router and a straight bit or using the table saw with the regular blade to cut rabbets

I made micro adjustments to the thickness of the rabbets using micro adjust on the router table raizer or using a small rabbet plane to take off a hair.

I find the thinnest edges around the ends of the zctp are too thin on both the supplied plastic plates and the use of flat head screws eventually splits this thin edge and the 3-screw pattern. Using the four screw pattern the edge is much thicker. But I had a very hard time getting the holes for the four screw pattern in the right place because I didn't have more than 6" calipers to measure the screw distances on the saw table. and no original plate with four holes to use as a template.

Someone eventually gave me one of the later factory accessory plastic plates uncut that has the four hole pattern I could use as a template.

[capncarl]

I remember making my zero clearance thick and replacing the blade with a 7 1/2” skill saw blade to cut the starting slot, then changing to the proper blade and cutting till blade was aprox 3/4” through. No sense cutting any deeper than you normally saw with, that can be deepened as necessary.

[SpinDoctor53]

I did some checking of the distance from the table to the surfaces the throat plate sits on. The surface the steel throat plates sit on varies about .0010" (.109 to .119) on my saw. The surfaces that the our ZCTP screws thread into range from .374" to .384" *. I checked all of this with a depth mic. The factory ZCTP's measure .360+/- a couple of thou over the countersunk holes. So tightening the hold down screws enough to hold it in place are going to tweak the plate somewhat.
Ways to fix this involve three different options.
1) Disassemble the saw and set the table up on a milling machine to machine the surfaces relative to the top of the table. Unless you have access to a milling machine probably out of the question.
2) Use a router to take very light skin cuts until you clean up the surfaces. This is is going to require either a very careful free hand or setting up stops to run the router body against.
3) Making up shims to even out the surfaces the that mounting screws thread into. And then super glue the shims in place.
Now comes the question. Just how close do we really want to get to Zero. And how flat is the die casting the table is made from in the first place. Chasing thousands of an inch could very well be a frustrating experience.
* The tapped holes the leveling screws are in.