# Calculating Start/Finish Cut Location

3077 Views 10 Replies 5 Participants Last post by  bobj3
I am brand new to woodworking and the use of the router. My initial questions are based on methods used to figure out how/where/what to measure to make my cuts in the correct location, should I use math, templates or jigs, or a combo of the two? A detailed description follows how I approached this initially.

I am making some shelves that will slope downward 30 degrees. To do this I am making wedges and want to attach these wedges to the underside of the shelf by cutting dadoes on the underside of the shelves. Cutting the dadoes the correct width, accurately and the most efficient way is the advice I seek.

My router base is round, 6" in diameter 3" on center, and I am using a 1/2" straight bit to cut my dado.
The first wedge will be 1/2" from the edge-- to figure out where to begin my first cut I added this distance (1/2") to the base diameter (6") divided the base by 2 and added 1/2 the width of the bit (1/4"), which left me clamping a speed square as a guide on my shelf at 3 3/4" from the edge which produced my first cut 1/2" from the edge. I realize the speed square is not the best choice for a guide, but I had nothing else handy and not sure what to use instead.My total wedge thickness is 1 1/2" so I have to move my guide (speed square) 1" in total to the right to make my slot the correct width.
I can continue this method of measuring to calculate where I should move my guide.... or is there another method not having to use math?

The second issue I am experiencing is having a round base, this seems like the ideal base, but if I move my hand slightly to the right or left, my cut now wonders or the cut is wider. Why is this, with a round base why does the bit not stay centered? How do I prevent moving the router from the exact position on my guide?

Thanks,

YLP
See less See more
1 - 11 of 11 Posts
Hi, YLP: welcome to the forum. a bit in a round base router may not be centered, or the router could have some runout, If you put an arrow or a mark on the router base
right where it rides your guide ( or square) you can then use the guide with the mark
for all the rest of the cuts. When making repetitive cuts I use guide bars and an edge guide, if they are going to be equal saped apart. After making the first dato the edge guide goes into that dato and lines up the next cut. Hope this helps. Woodnut65
Hi YLP

Sounds like a fixture and a brass guide will do the job you want to do.

The neat thing about a router is that it will do a job again and again making the same cut and the key to that is fixture/template.
Use the template to put in a 3/8" wide and 3/8" deep dado then because it sounds like you are using 3/4" thick stock, use a rabbit bit to put a 3/8" wide 3/8" long teton on the end of the shelves,then remove a small part on ea.end of the teton so you can hide the joint in the dado slot.
I would use a book type jig/fixture that I could side the stock into place with a indexing block/pin that would line up the slots right on the button then plunge the bit in and make the dado cut(s).
Jig would be one board on the bottom and one board on the top with the 30 deg.slot to run the brass guide in to made the dado slot.(just like a book with out pages) make a wedge to lock the side in place and use a setup block to set up the spacing for ea. dado, make the 1st cut then remove the wedge then move the stock forward to the stop block/or pin stop put the wedge back in place and made the next dado slot and so on till you have what you want .
If you don't have a router table just use your jig saw to cut the hole for the brass guide to run in.... but it needs to true , sand it or file it,what the guide runs in must be true ,it will copy what every it sees. (nick or a bump)

The math is below ▼ ☺
http://www.routerforums.com/1812-post9.html

Hope this helps.
See less See more
For consistent accurate cuts that don’t move of off the cutting line, you need to make a router base plate that is few inches wider than the router base for good support and has one perfect flat side. The flat side has to be perfectly as in 100% aligned to the routers flat side as you see in the picture. Then you measure from router bits cutting edge to the flat side and that will always be your cutting line. If you decrease the router bit’s diameter, this cutting distance will increase as in going from ½ router bit to ¼ router bit. If you increase the router bits diameter as in ¾ or 1 inch then the distance will decrees but will always be perfect. I have use this the past two decade for joining boards and making perfect cuts since I don’t have a table saw or jointer or anything else.

#### Attachments

• 327.3 KB Views: 138
• 324.3 KB Views: 226
See less See more
2
Thanks everyone,
I will try each approach offered. The first one I would like to work w/ is the fixture and brass guide by bobj13. I actually have a 7 piece template guide set... what to do with it I have no idea. I do not have a brass guide. It would be extremely helpful for photos to show/explain visually how this would work. I am heading off to visit the links that bobj13 has in his reply. Any other advice is welcome.
Hi YLP
Have a look at this post

With this jig you can use any bit dia up to the width of your dado.

niki
Woodnut,
I follow you completely, thanks. I found a couple of videos that helped make your point very clear.

YLP
Bobj3,
Use the template to put in a 3/8" wide and 3/8" deep dado
When you recommend using the template, what are you referring to? Am I to make a template?

then because it sounds like you are using 3/4" thick stock, use a rabbit bit to put a 3/8" wide 3/8" long teton on the end of the shelves,then remove a small part on ea.end of the teton so you can hide the joint in the dado slot.
If you have a photo of the concept that would be nice to see. I think I understand, but to verify what you are conveying is what I am thinking too.
I would use a book type jig/fixture that I could side the stock into place with a indexing block/pin that would line up the slots right on the button then plunge the bit in and make the dado cut(s).
No idea of what you mean here,.... indexing pin?
Jig would be one board on the bottom and one board on the top with the 30 deg.slot to run the brass guide in to made the dado slot.(just like a book with out pages) make a wedge to lock the side in place and use a setup block to set up the spacing for ea. dado, make the 1st cut then remove the wedge then move the stock forward to the stop block/or pin stop put the wedge back in place and made the next dado slot and so on till you have what you want .
If you don't have a router table just use your jig saw to cut the hole for the brass guide to run in.... but it needs to true , sand it or file it,what the guide runs in must be true ,it will copy what every it sees. (nick or a bump)
The last part is beyond my comprehension for the time being and I am having difficulty visualizing your idea here.

Best regards and thanks,

YLP
Router is Still my Name-
1) you are measuring from the edge of the bit that is flat. But will this measurement change when the bit spins, getting wider on the rounded portion of the bit? If so this seems to be harder to get a correct accurate measurement. This was one of the problems I was dealing w/ initially. That is why I took the approach of measuring the bit from edge to edge and dividing it by 2. Do you think this is a good approach?
2) making my own router base- where do I find the material to make it out of and what material is it? What do I cut it with?

thanks,

ylp
Thanks Niki,
This does a great job of showing off your solution and is exactly what I am trying to get figured out. I will play w/ this some more in a couple of days and get back to you.

Cheers,

YLP
Hi YLP

"indexing =
# Something that serves to guide, point out, or otherwise facilitate reference."

Besure to make the book template so you can unscrew the top part so you can flip it over to do the right side as well, just like the left side .(so you can have match set)
Make the indexing block so the pin can side out of the block, 3/8" dia.dowell pins or roll pins ,will work great for this job. (2 ea. bottom and top of slot) but they must be right on . also see the quick index block below.

see item(s) below ▼

#### Attachments

• 29 KB Views: 144
• 14.4 KB Views: 136
• 21.3 KB Views: 127
See less See more
3
1 - 11 of 11 Posts