What are Bushings for?

[radhak]

After woodworking for 6 months, and using routers for the same time, this might seem like a silly question, but I am not gonna know unless I ask : what exactly are router bushings for?

Last week I bought a Milescraft signcrafter that helps make signs (letters/numbers) and it had two plastic bushings, which, after using, seems to be for guiding the router-bit along the template. So are all bushings used for templates? I thought router-bits with bearing guides would help template-routing, but of course looks like I might need to hunt for a bit with a very short (or adjustable) bit-length for some templates.

So if I buy a bushing set, it would be helpful for template-routing where bearing-bits are unusable, right? Say, with a dovetail jig or something similar (when I get around to buying those)?

Problem is, the plastic bushings I used imposed an offset from the template, so the routed sign is much 'thinner' than what the template shows, and am guessing even the brass ones would have the same 'feature', leaving a learning-curve to get it line up accurately. And of course, most of the routing seemed to be 'blind', ie, I was not able to see what I was doing 100% of the time. Is that how it's supposed to be, or was it just my lack of technique/experience?

Finally, I might need to buy new bits just for the bushings, seeing the narrow openings. I am the proud owner of the Holbren 35-bit set, but can easily see most of them may not fit in bushings.

thanks.

[LarryG]

So if I buy a bushing set, it would be helpful for template-routing where bearing-bits are unusable, right? Say, with a dovetail jig or something similar (when I get around to buying those)?

Yes, that's exactly right.

The offset you noticed is part of the way guide bushings work, and always require some arithmetic. The template that the bushing follows will be smaller than the desired dimensions of the finished piece, to allow for the difference between the bushing's diameter and the bit's diameter. The exact amount, of course, will depend on the diameters of these two elements.

As regards the bits in your set ... bushings are typically only used with straight bits, so that narrows the field considerably.

[cabinetman]

Some of the bushings I use are based on the full diameter of the bushing, so when used in a zero clearance template there is no error. Others are a thickness bushing that acts like a bearing on a bit, which spaces the edge of the bit to the template. I have on occasion used a decorative bit with a bushing when I need a profile on the inside of a cutout, when the bit doesn't have that capability, and I have to make a template for the pattern. For an outter edge detail, I may have to make a template for the same reason.



"I'M NEVER WRONG - BUT I'M NOT ALWAYS RIGHT"

[LCHIEN]

I agree with both CAbinetman and Larry.
Bearing guided bits are best (easiest) to use when you have an exact template.

Templates and bushings are used with mostly straight bits las Larry said, or sometimes with rounded end or pointed end bits for lettering templates and the like.
Yes, the offset has to be taken into account, and lettering templates are usually made with a specific bsuhing dia. in mind to follow the letter strokes exactly without having to make two passes, you chose a bit diameter to get thicker or thinner strokes or lines in the letters.

If routing openeings and more complex shapes then you have to use a bushing size and bit dia with the difference in diameters intended by the template designer to get the correct sized opening and
use the correct bit dia to get a specific corner radii and you will also have to make multiple passes to clean out the center area away from the bushing edge.

[Tom Hintz]

I have a story on using router guide bushings at the link below with photos and more detail that might be of interest to you.
These are very handy tools that can make cutting lots of similar pieces easy or just getting one just right less difficult.

http://www.newwoodworker.com/guidebush.html

[MilDoc]

Some of the bushings I use are based on the full diameter of the bushing, so when used in a zero clearance template there is no error. Others are a thickness bushing that acts like a bearing on a bit, which spaces the edge of the bit to the template.

You lost me on that one Cabinetman. Can you explain further, provide examples, or links to the differences?

[cabinetman]

Paul

In explaining the differences, I have to first mention the purpose of a router bearing. For example, a slot cutter will mortise/rabbet a specified depth depending on the diameter of the bearing. If a smaller bearing is installed, the bit will cut deeper, and the reverse of this premise is a larger bearing will give a more shallow cut. I'm talking about basically a distance between what the bearing rides on and the cutting edge.

For bushings, a predetermined distance depending on the template, as in a dovetail jig allows the cut as per template. The distance between the edge of the cutter and the edge of the template can vary depending on the size (diameter) of the bushing. The variety of bushing sizes and bit diameters give versatility to template making, and pattern design. Some procedures can be done with templates and router bits with bearings. Since bushings are flat to the base, this allows for thin templates to be used without the height of using a bit with a top mounted bearing. I haven't found enough combinations in that configuration to be available.

I don't know if my explanation answers your question, as it may sound like a redundant answer. I'm probably not that good in explaining things.



"I'M NEVER WRONG - BUT I'M NOT ALWAYS RIGHT"

[guycox]

And all this time I thought a bushing was what you did with a really bad tool purchased at a Garage sale. -- Toss it in the bushes and leave it

[radhak]

Thanks

Thanks for all the advice, guys. Always useful and relevant. And Tom, your article is great - I might get away without having to buy a book!