Determining Chamfer "Size"

[Hoakie]

I was wondering how to correctly interpret chamfer measurements. The plan for the ShopNotes assembly table calls for a 1/8" and a 3/8" chamfer on the different pieces. Does this mean the depth of the chamfer is 1/8" or the hypotenuse should be 1/8".


Also, what is the best way to set depth on a bit with a guide? Trial and error or is there a magic trick. I've seen setting up a test block with common chamfers that you can use to quickly set up but was wondering if there was an different way?

Thanks
John

[sparkeyjames]

None of the above. It's the measurement across the face of the chamfer. Say you want a 45 degree chamfer that is 1/8 inch. You would set up your router/saw whatever to leave a facet 1/8 inch across.

http://en.wikipedia.org/wiki/Chamfer

sparkeyjames.

[LCHIEN]

How to interpret chamfer dimensioning

All chamfers I've seen specified are done by the short depth dimension as shown in this example from a CAD tool:

http://www.cadlab.tuc.gr/proehelp/part/example4.htm

So per your original question, it's the depth, not the hypotenuse.

[LCHIEN]

Setting blade and bit height/cut depth

Also, what is the best way to set depth on a bit with a guide? Trial and error or is there a magic trick. I've seen setting up a test block with common chamfers that you can use to quickly set up but was wondering if there was an different way?

Thanks
John

Order of best to least:

I use my height gauges, preferably.

http://www.bt3central.com/showthread.php?t=29719&highlight=height+gauge

I adjust the height of the blade or the bit and set it, then always make a test cut and check with calipers.

An alternate plan is to use set up bars of the appropriate height next to the bit or blade, then slide an object over the top of the bar and it should just tick the bit or blade - lower a hair and when you don't feel the tick anymore, its set right. Again, a test cut and check with calipers!

http://www.rockler.com/product.cfm?page=16399

You can also buy inexpensive step gauges - looks like an inverted ladder with steps at 1/16th intervals. - hold next to the bit and raise the bit until it pushes up on the step. Works OK, not my favorite.

http://www.amazon.com/General-Tool-G3467-Gauge-Table/dp/B0000DD1PU

Did I say make a test cut? Usually right on-prevents mistakes. You only have to cut about 1/2" to check ...

[Tequila]

I'll second what Loring said - the chamfer measurement is along the short dimension, not the hypotenuse.

[LCHIEN]

More hints for small chamfers.

In reality, esp. for woodworking, a small edge chamfer really doesn't make a whole great lot of difference whether you measure the depth or the hypotenuse. The hypotenuse is 1.4 x longer than the depth.
So if the plan calls for a 1/8" chamfer and you mistakenly make the hypotenuse 1/8 then the depth will be about 3/32, only 1/32 off the intended measure.

as for making the chamfer, I assume you have a 45 degree chamfer bit with a bearing or a fence and a 45 degree bit with no bearing. In either case the depth is set by the height of the bit. The way to get the exact measured depth is to mark the workpiece at the 1/8" from the edge using a marking gauge or similar. Then run it by the bit with minimal height, adjust the bit upwards for subsequent passes until the edge of the chamfer hits your mark. For the rest of the work, a 1/8" chamfer can be taken in a single pass (total material being removed is small), however, I always make additional fast passes at the same depth to make sure the edge is clean and straight - until making a pass results in audibly no material being taken off. In the case of such a small chamfer, any point where you wantered off the bearing or fence just a little is obvious.