Sliding Angle Grinder Jig

A lot of my recent projects require using an angle grinder on metal to make my cuts. In order to speed up my process and get better straight cuts, I decided to make my own jig to mount my angle grinder on. I get that with a steady hand and patience, you probably don't really need this, but anyone who knows me understands I have little patience and drink a lot of coffee. Therefore, I required the following:

1. Easy to build
2. Limit "extra" purchases aka keep cost to a minimum
3. Able to make plunge cuts
4. Able to make sliding cuts

I did a lot of research for this build based on my needs. I will leave #3 and #4 above as separate steps below in case you would like to stop at one or the other. This took a lot of problem solving but let's get to the good part!

Scrap wood

Rails (I used 3/4-inch EMT conduit)

If you are using 3/4-inch EMT conduit, you will need an 18mm drill bit

Slider (I used 3/4-inch PVC pipe)

Angle grinder with cut-off wheel

Split-ring hangers

Rubber material

Various hardware like screws, nuts, washers, bolts, etc.

Wood glue

Metal flashing

Paint

Marking tools

Measuring tools

Angle iron (for getting a 90-degree fence to cut against)

This video serves two purposes:

1. showing my build process, and
2. showing my problem solving (of which, I needed a lot)

For my build, I wanted the best of both worlds; plunge and sliding cuts, when needed. The problem that came back at me the most was the depth of cut I had to work with, and this is something you need to consider, too. Your standard angle grinder will often be equipped with a 4.5-inch cutting wheel which will only yield 2 1/4-inches of cutting capacity (pic 1). This leaves you with a handicap of usable depth.

Pic 2 & 3 shows that the hardware you choose can minimize your depth of cut but if you are simply using this to mark/score metal, you likely don't need to stress on the depth as much as me. The conduit hanger on pic 2, while good to mount EMT, will lose about an inch. The spring hinges in pic 3 will also deplete an inch while the regular hinge will take away about a 1/2-inch. If combining the conduit hanger/spring hinge is the route you choose, just understand (depending on the manufacturer, of course), you will only have 1/4-inch of usable angle grinder cutting wheel. . .

Looking at pic 4, you can start to get a idea of my hamster spinning the wheel in my head. My OG idea, was to make a rail that the angle grinder could slide back and forth on using PVC pipe to slide on the EMT (This worked well in my camera slider instructable). The plunging action would be accomplished with either a stand alone spring hinge or a combo of the regular hinge and an added spring. I replaced the EMT conduit hanger with a split ring hanger to gain ~3/4-inch in my cutting paths. Having the EMT "rails" parallel and mounted as close to the edge of the plywood it is mounted to will also maximize my cutting depth. The 2 split ring hangers would be connected in their center taps with a 3/8-inch threaded rod and associated nuts and washers (pic 12).

Seemed simple enough, so I got to it.

I cut the EMT in two equal lengths with a pipe cutter, chopped the PVC with a saw, drilled [18 mm] mounting holes in scrap plywood, and put together my split ring slider (pics 5-12). Pic 15 shows me gluing the pieces together.

To mount the angle grinder, my idea was to use some scrap metal, bent at a 90-degree, and mount that to the angle grinder hand screw hole. Pic 13 shows a store bought mount I had from way back in the day. It isn't long enough to work with this project and is only shown for demonstrational purposes. Being that I am a glutton for punishment, I decided to make my own and prototyped the dimensions with scrap card stock (pic 14).

If you only need the plunge cut, the ways to go about this type of cut with your angle grinder would be to use some sort of spring action. This could be using a hinge with an added spring to keep tension. It could also be combined by using a spring hinge like you would use for your screen door or a fence door. Slow and methodical is the name of this game.

The hinges shown in picture 1 show a regular door hinge on the left and a spring hinge on the right. If using a regular hinge, you should install a spring to maintain tension on your angle grinder to spring back, protecting your work.

You don't need the EMT conduit shown in the last step and really you could mount your hinge using scrap wood and a hose clamp. Colin Knecht's build on WoodWorkWeb shows a really good example that I kept coming back to for ideas.

For this type of cut you also have a few options. The easiest way in my opinion is to buy a set of linear rails and attach your angle grinder that way. I also saw folks making their own set of rails or modifying other tools, like a manual tile cutter. These can be mounted horizontally or vertically. I hybridized this to have a rotating action to give me a plunge and a sliding cut. With a rigid mount, this can be a really simple and cheap build.

To mount my angle grinder I cut out a 40mm x 105mm piece of metal (pic 1-2), scored it at the 65mm mark and bent it at 90-degrees. A hole was drilled, cut, and filed (pics 3-8) to place in between two nylon washers (pic 9).

Now the problems arise:

1. The slider doesn't slide as smooth as a light weight camera phone. SOLUTION: add felt pads inside the PVC and smooth the EMT.
2. And this is the real problem, the angle grinder position and weight are flexing my metal mount. I mean this was not a great situation to get reproducible cuts...SOLUTION: get a more rigid mount.

Easier solution to #2 would be to weld a rigid mount that can still be attached to the angle grinder mounting hole (like 80% of the videos I watched on YT), but the problem with that is my welding skills are lacking and I don't have access to a weld shop (A problem to most people I am assuming).

I DO have access to copious amounts of HDPE and a press to mold blocks...

Disclaimer: I understand people don't have access or want to reuse HDPE like me. If you don't have this, store bought wood is fine (in proper Ina Garten demeanor :P )

I got the length of the angle grinder with my calipers, melting an appropriate amount of HDPE shreds, heated them in my toaster oven and panini press (shout out to Brothers Make!), and press the devil out of it (pics 1-9).

I used a 64mm hole saw to drill out where the angle grinder will sit and this is a little too large. I did that on purpose to allow a rubber piece to sit in between with the intention that this would inhibit the grinder from twisting around in the "slippery" HDPE. Again, you can glue and cut scrap wood to accomplish the same thing. Don't yell at me like, "Oh suuuuure, all I need is 75 million dollars in tools and a plastic recycling plant in my garage..."

My grinder will now go from horizontally mounted to vertically, and I will do so by drilling my hole in the center of the plastic (pic 10) and moving my split ring hangers from facing each other to facing outward. My old mounting bracket was modified (pic 11) to hold the plastic angle grinder mount (pic 12). This is just juuuuust loose enough to allow the grinder to pivot up and down in order to get my plunge cuts. Obviously, it will slide on the rails back and forth for sliding action. Pic 13 shows the rubber piece and the angle grinder is held in place with an additional bracket (pic 14).

Pic 15 shows the makings of a [soon to be] completed project...whew! It's about time!

Now I need a base to mount this bad boy! Using more scrap wood, I got three pieces and screwed them together in order to have a channel the cut-off wheel can slide through (not touching, of course). The slider was installed vertically (pic 2), "angle irons" were mounted for 90-degree cuts (pic 3-4), and a piece of metal flashing just large enough to cover the platform (to minimize fires...sparks and wood, ya know) was installed (pic 5-6). After a quick paint job (pic 7), this baby was ready to test!

Pics 1-3 show a piece of rebar getting cut on the 90.

Pics 4-9 show my plunge/sliding cuts to get my Nevada cut out of the broken saw blade.

You can see from pic 9 that these cuts are nice and straight. No shaky hands for this guy...well, I still have shaky hands but at least the jig will guide the grinder to compensate :)

At this point you still may be wondering, why? Why make this? Wouldn't the time spent sliding be equal to a wobbly cut ground down on the sander??

Yes and no (IMO). I feel that with my level of experience (novice like maybe a level 5), the time I make up at the belt sander is a gain in my shop. I don't have to spend nearly as long sanding away at the belt grinder and plus, I made this baby out of common materials but mostly scraps in my shop. How cool is that (again in Ina Garten voice)!?!

And that's that. That is my weekend project. I hope you find it useful and I you will see my scrappiness on the next one. Thanks for sticking with me.