How do I cut a long slot in plywood?

[William Burgess]

I am trying to make a 3-in-1 cross cut sled which I found in a shopnotes. I am currently trying to cut a slot in the middle of a plywood peice which attach to the top of the sled. If you look at the pictures (I found these on the web)

http://futsing.homeip.net/woodshop/cutoff_sled_pics.html

You will see the top peices have a long slot right in the middle of it. The slot is 3/8" wide. How do I cut this slot? I was thinking with a router bit, but I don't have an edge guide (but I do have a router table). Is this something I could do with a router table? Drill some holes at the end, line up the fence to the right distance and insert the bit into the hole and slide it along until I reach the spot I need? And is this safe/what should I be careful for? I am very new to woodworking and am trying to figure out the best way to do this. Thanks!

William

[hank dekeyser]

William, welcome to the wonderful world of woodworking. Take what I say with a grain of salt. When I started this "hobby" I too wanted to make every jig, gizmo, add-on I could find. And I did make quite a few goofy jigs and stuff. Almost all of them ended up in the woodstove after gathering dust on the shelf. Ask yourself, what do you want to build / make out of wood, and are the fancy jigs neccessary to accomplish that ? I say this because I see similar jigs in the magazines frequently and how everyone says they're the best tool they have for their table saw etc. - I built one, and then never used it, I can do the same thing with a piece of wood bolted to the mitre gauge and a stop block. (or my sliding mitre saw, which resides next to the TS)


Now to answer your question. Cut it with your table saw. Build the base, attach the runners, THEN use the TS to cut the slot. (you can flip it over and use your mitre gauge to make another cut on each side making it 3 blades wide) THEN attach the rest of the gauge to the base paying attention to align it perfectly to the saw blade Give some thought to being able to make minor adjustments to the set-up in the event you need to (if you get a kick back it can reaaly mess up the alignment) I'm sure WOOD magazine did this once upon a time and has a step by step guide to follow.
Be careful and wear your safety glasses.

[Ken Fitzgerald]

William,

Yes I would do it as you describe.

Lay it out on the pieces. Drill the holes at each end.

Put the appropriate bit in the router. Lay the piece over the bit and adjust the fence on the router table.

Then I would mark on the fence the start and stop point relative to the ends of the top piece.

I would remove the piece from the bit once the fence is set. Turn on the router and drop the piece down over the bit...trying to hit the hole but error on the "waste" side that will be routed out...all the while holding it snug to the fence while dropping it down. I am a little nervous about starting the router up with the piece held over the bit. When you reach the hole at the other end, lift the piece clear of the router bit and shut the router off.

Be extremely careful. Spinning bits are hungry! Don't feed them flesh.

I have actual routed mortises for cabinet door frames that way.

Be careful...Good luck...post pictures when you are done.

[glenn bradley]

+1 on drill the end holes using a fence on your DP for accuracy. Use the piece and the one of the holes you just drilled to align your router table fence and bit to match that offset. Set up stops on your fence so that your routed cut starts and stops in the drilled holes. Lower your bit to take about 1/8" cut and make your first pass left to right. Raise the bit about 1/8" and make another pass left to right; repeat until you have your slot cut all the way through. Take care to really control your material as this is a "captured" cut. By that I mean your material is trapped between the bit and the fence. Always reason for extra care.

[Kent A Bathurst]

Jigs and fixtures are not treated like pieces of art in my shop - they are functional tools. I don't have a router table. Having said all that, use a couple strips of plywood as your router edge guides, and screw them to the ply base.

If the residual holes are simply too much to bear, drill 'em out, and plug them with a contrasting dark wood. Maybe some matching stringing around the perimeter of the base, and edgebanding on the fences? Just kidding..........sort of.:p

[Pat Barry]

I tend to agree with Kent. I have used the plywood (straightedge) method many times and it works well. Here are a few tips from school of hardknocks: Make sure you know precisely the distance from the router plate edge to the closest edge of the bit. Easiest way is to make a test cut in scrap. You need this distance to calculate the offset need for the fence. Next, carefully lay out your intended routed groove. Measure, re-measure and if needed measure again to set the straightedge in the correct location. Then clamp it in place - now obviously having a fairly wide straightedge is helpful here so your clamps can be positioned well out of the way of your router. (The clamps need to be on the opposite edge of the straightedge from the side you intend to use. Route the channel carefully, using multiple passes with increasing depth as needed and make sure you maintain contact with the straightedge - so go slow.

[Erik France]

I'd probably cut it on my tablesaw, maybe using a dado stack, more than likely just a few pases with a regular blade. My router table isn't all that big, so I wouldn't feel good about doing it there.

As other have mentioned, a router and straight edge will work. If I were to use my router I'd use it on a sawboard. I've got a sawboard that will work with my circular saw on one side and the other side is set up for my fixed base and a 1/4" bit. The board is a length of white bathroom wallboard (3/16 hardboard with a melamine like coating) with a straight 1x2 down the middle. A sawboard is easy to make and helps to reduce tearout with a circular saw. The best thing is that you don't have to measure offsets from your cutting line for a straightedge fence. Just put the edge of the board onto your line.

[John Coloccia]

You can use a straight edge for sure, however my favorite way of slotting is now with a slotting jig. To make the jig, I take two pieces of MDF that are straight. Between them I glue a piece of MDF on either side that is the same width as one of my router bushings (I usually use a 1/2" bushing to route a 1/4" slot, for example). Now I have a channel for my bushing to ride in. The last touch is mark centerlines on either side so you can line up the jig. I also have a couple "spare" 1/2" blocks with centerlines marked so that I can place it in the jig for alignment purposes when the jig is much longer than the slot.

This sounds complicated, but the jig literally takes about 2 minutes to make, and I found it's extremely accurate and easy to setup. I just use a few squares of double sided to hold it down. What's nice is that the ends of the jig act as stops.

Honestly, I'm surprised no one offers this style jig with movable stops as it's superior to the straight edge, IMHO. Hmmmmm....

Here's an example of one of mine:

http://i913.photobucket.com/albums/ac335/jcoloccia/Slotting%20Jig/Photoon2011-01-29at1410.jpg

[Erik France]

Honestly, I'm surprised no one offers this style jig with movable stops as it's superior to the straight edge, IMHO. Hmmmmm....
Woodhaven sells some expensive ones. http://woodhaven.com/category/27914119281/1/Dado-Jig.htm

[John Coloccia]

Woodhaven sells some expensive ones. http://woodhaven.com/category/27914119281/1/Dado-Jig.htm

So they do. I didn't know that. You can make a lot of "John Jigs" for $200. LOL.

[Mike OMelia]

You can use a straight edge for sure, however my favorite way of slotting is now with a slotting jig. To make the jig, I take two pieces of MDF that are straight. Between them I glue a piece of MDF on either side that is the same width as one of my router bushings (I usually use a 1/2" bushing to route a 1/4" slot, for example). Now I have a channel for my bushing to ride in. The last touch is mark centerlines on either side so you can line up the jig. I also have a couple "spare" 1/2" blocks with centerlines marked so that I can place it in the jig for alignment purposes when the jig is much longer than the slot.

This sounds complicated, but the jig literally takes about 2 minutes to make, and I found it's extremely accurate and easy to setup. I just use a few squares of double sided to hold it down. What's nice is that the ends of the jig act as stops.

Honestly, I'm surprised no one offers this style jig with movable stops as it's superior to the straight edge, IMHO. Hmmmmm....

Here's an example of one of mine:

http://i913.photobucket.com/albums/ac335/jcoloccia/Slotting%20Jig/Photoon2011-01-29at1410.jpg

Yeah, thats good John. Now show me how to do the same exact thing with a curved slot, say a figure "S". I ask this because I asked a similar question earlier, and what you have in your hands is exactly what I did. But it did not work. (for curves).

Sorry for the hijack. I too would use a guide (single edge). Joint an edge then clamp or screw down. Or pin with brads (less visible damage). It works all day long. If you have a loose router around, that is.

Mike

[John Coloccia]

Yeah, thats good John. Now show me how to do the same exact thing with a curved slot, say a figure "S". I ask this because I asked a similar question earlier, and what you have in your hands is exactly what I did. But it did not work. (for curves).

Sorry for the hijack. I too would use a guide (single edge). Joint an edge then clamp or screw down. Or pin with brads (less visible damage). It works all day long. If you have a loose router around, that is.

Mike

If you did it on a curve by cutting the curve down the center of two pieces, and then separating them, it won't work because the inside and outside profiles are different, so you'd get a lot of binding. Is that what happened or is it something else? I've never tried it on a curve. I'm curious what went wrong.

To get the right profile, cut one of the profiles and the use that to trace the matching profile. They sell little "offset" marker thingies that you can stick a pencil point in and trace the curve, but I usually just wing it with a compass for this kind of thing. The little offset thing would be better (it's nothing but a disc with a hole in the middle for a pencil point). My compass has a flat on the leg that makes it easier to stay perpendicular to the curve. it's good enough considering I do this maybe once a year.

Oh, and sorry for the re-hijack :P

[William Burgess]

Well I finished the cross cut sled. I cut the slot on the router table with a 3/8 bit running it over twice. It went pretty well. I am not completely satisfied with the sled as I had some chipout working with the plywood, but it does its job. Hank, I understand completely what you mean. Half way through this sled, I thought to myself, is this really worth it? Wouldn't a piece of plywood with a front & back and some runners do the job, and be much more simple. But, by that point I was half way done and wanted to finish it. Who know how much I will use this as I have a compound miter and a incra 1000se, but it was a learning experience. This is really just my 3rd peice of real woodworking, I made a toy train set for my daughter and a simple cutting board and now this. Next time I will defiantly stick with a simple jig which gets the job done and not a fancy one which does everything. Thanks for all the advice.




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[Curt Harms]

Yeah, thats good John. Now show me how to do the same exact thing with a curved slot, say a figure "S". I ask this because I asked a similar question earlier, and what you have in your hands is exactly what I did. But it did not work. (for curves).

Sorry for the hijack. I too would use a guide (single edge). Joint an edge then clamp or screw down. Or pin with brads (less visible damage). It works all day long. If you have a loose router around, that is.

Mike

Not John but I'd probably look on this forum for somebody with a shopbot or other CNC setup to create the jig.:)

[Mike OMelia]

Not John but I'd probably look on this forum for somebody with a shopbot or other CNC setup to create the jig.:)

Both John's and your point are correct. After I figured it out, I realized a rolling template whose diameter is the desired gap width was the simple answer. Its funny how this stuff works out when yo stop and think for a moment.

TO the OP, what did you decide?

[Doug Shepard]

I've mostly used a router and straight edge clamp to slot through things but occasionally I've cut them on the table saw with a dado stack. With both start and end marks on the fence to indicate where the dado stack is at when cranked all the way up, lower the blade and line the work up with the marks. Then power up the saw and raise the dado all the way up and feed the work, stopping at the the end mark then power off the saw and wait til it's come to a full stop. Then a couple cuts with a hand saw and chisel to square up the ends of the cuts. The router usually gives a cleaner cut but at the expense of making multiple passes. The dado method is way faster though.

[Charles Lent]

I think you have missed an important point of the reason for making this jig. The table saw must be used to make the cut for it to work correctly: 1. To make the blade cut and the rear fence at perfect right angles to each other. 2. To provide a zero clearance insert type of function to minimize tear-out when cutting the stock. You should be able to cut stock at a perfect 90 deg with little to no tear-out when the jig is used. If you build the jig any other way you won't achieve the results intended by it's design.

Charley

[hank dekeyser]

To the OP - well done ! By no means was I trying to disuade you from building it. merely passing along my personal experience. I built ALOT of goofy things mainly just for the sake of building them. Plywood is cheap, and if you're like me you have more time than money. Half the fun is in the building it and figuring your way out through it. There's no such thing as a "useless jig" just one that doesnt get used much. Being older (and hopefully wiser) now - I tend to just build stuff I need or will use. Besides, I'm out of shop space - gotta take down some trees this Summer and add on (again) Have fun