Might depend if you are using the router handheld or in a table.
If I'm using it hand held, I like to have the template on top of the wood and use a top bearing.
If I'm using the table, then I also like to have the template on top of the wood, but use a bottom bearing (which ends up at the top as the router is upside down).

 

OK. I'm using it in a table, and was thinking that having the template under the work piece, would be nice, so that I don't have to slide the work piece against the table, and maybe scratching it. But I guess sliding the acrylic template against the table over and over again, will be worse...

Also, the table should be so smooth that scratching isn't a problem....

Thanks!

 

Katana® Rabbeting Router Bit Kits, Round Nose / Core Box Router Bits, Flush Trim Router Bits

MLCS Katana Flush Trim / Pattern Routing - YouTube

Spiral Cut Flush Trim Bit - YouTube

Top & Bottom Bearing
Flush Trim/Pattern Bits
Katana® Flush Trim/Pattern Bit Kits
MLCS Flush Trim and Shear Angle Flush Trim Router Bits

===

 

I saw that bit, and didn't understand why there were two bearings. The video shows it quite clearly. Maybe that's the one I should go for. My body blanks are usually 46mm thick, so a 2" cutting height will be enough..

Tommy

 

Hi Tommy:

I have, and use, both. I don't have a double bearinged bit. I try to reserve the shaft-mounted bearing for templates. The bearing mounted in the tip I use for table mounted templates. The template could be identical. My preference is to use the template on top of the workpiece. Others may have different philosophies and use it on the bottom. If you're using an overhead pin router, the template must be on the bottom. Much more difficult to follow in that position. I like seeing what I'm doing - pin routers obscure the template.

The double bearing bit is a cheap way to accomplish both, top or bottom mounted template, freehand or table mounted.

 

I am now thinking that maybe that double bearing bit is best for you. The main advantage is that when routing a shape for a guitar body, you will end up routing against the grain in many places. With the double bearing bit, you can flip the work piece with template attached and rout in the best direction for the grain. You might have to re-adjust the bit height depending on thickness of template and work piece.

 

What do you prefer? Flush trim bits with top-bearing or bottom-bearing? Are there any pros or cons that I should know about?

I'd second the double bearing bit suggestion.

Some solid lumber consistently breaks when routed in the wrong direction with respect to the grain (I learned that the hard way).

This is good:

wood grain
\\\\\\\\\\
O bit (rotates clockwise)
hand-held router moves ->

the wood fibers move out of the way like on a feather board

This is bad:

wood grain
//////////
O bit (rotates clockwise)
hand-held router moves ->

the fibers catch like on a feather board

Where curves cross the piece going from good to bad you want to flip the work over so that you can keep moving in the right direction to avoid breakage without making a climb cut.

Solutions are to flip the work in the pattern (which only works for symmetric pieces and is easiest if they're held together with toggle clamps) or flip the work and pattern over.

In the later case you need both flavors of bits (in which case you need to change them) or one bit with both bearings so you can just change the height.

 

God I love this forum. You don't get stuff like this anywhere else. Bang on! My solution was always to leave 1/32" to be finished by hand. Now, I know better.

Thank you.

 

"Are there any pros or cons that I should know about?"
*****************************************
For stock as thick as yours I'd use neither.
A plunger, collar and stout (>3/4"CD) straight cutter would allow safer stage cutting.
Moreover, given light cuts, you could climb cut, eliminating most tearout whilst passing through the end grains. This would best done with the hand router. Messy indeed but good results.

 

Any consideration of using a MLCS Daisy Pin Router

"Are there any pros or cons that I should know about?"
*****************************************
For stock as thick as yours I'd use neither.
A plunger, collar and stout (>3/4"CD) straight cutter would allow safer stage cutting.

Hi Tommy,
I agree with Pat on the use of a larger straight cutter. I've been using a MLCS Daisy pin router with some success, permanently attached to a Rockler table. It cost about $50 and not $2500 as for a dedicated bottom pin router. I use the larger 1/2" pin for my work.
The maximum pin size is 1/2", but a 1/2" ID to 3/4"OD bearing could be mounted on the 1/2" pin if one wanted to use to a 3/4" straight cutter.
The pin arm assembly could also be raised on blocks if the pin is too low for the work.
Usually the router table is smooth enough if everything fits.
This is just another option, if you like the results one gets from a larger straight cutter.

Mark

 

By definition, a flush trim bit has a bearing on the bottom and a pattern bit a bearing on top (of the bit), no matter whether used in a handheld, table, or pin router.

I don't understand why a pattern must be on the bottom for a pin router. Wouldn't this be the same as using a handheld router?

I agree that there's nothing wrong with a climb cut for the final 1/32-1/16 to get a clean edge.

Flipping the workpiece with the pattern attached is not always easy. If you use double stick tape, it can be done. You'd have to use pencil marks on the pattern and workpiece to indicate cutting side (based on grain direction of work). Personally, I'd try to avoid flipping.

 

By definition, a flush trim bit has a bearing on the bottom and a pattern bit a bearing on top (of the bit), no matter whether used in a handheld, table, or pin router.

I don't understand why a pattern must be on the bottom for a pin router. Wouldn't this be the same as using a handheld router?

An overarm pin router is a lot like a drill press or vertical mill with a plunging spindle on top. Pattern work is done with a table mounted pin that engages a pattern beneath the work

http://www.grizzly.com/products/Overarm-High-Speed-Router/G8030

 

Gets confusing depending on the which way the router is mounted?

 

I will be using a bandsaw to rough cut the body, leaving maybe 1/8 or less wood to be routed away. For the different cavities on the body, I'll be using a plunge router with templates...

Tommy

 

Hi Tommy:

I've gone back and reread all of your posts in this thread. I'll try to clear up all of the issues for you.

1. I don't know what you're using as a router table but the last thing I worry about is scratching it. I'm far more concerned about blemishing the workpiece. But, I'm also doing research on the best layout for a table top so I consume tops frequently.

2. The double bearinged template bit has some good possibilities. See Drew Eckhardt's post above. That's the best advice I've ever seen on this topic.

3. There are 25 ways to mount and use a router. Selection of any method is purely personal preference. Personally, I don't see pin routers being any advantage over any other mounting method, but then, I don't have one and bungle along quite nicely in spite of that handicap.

4. You're working with guitar bodies. For the outside of the body pattern, Drew's suggestion is spot on.

5. for thicknessing the body I'd suggest that you create a pattern and use a pivot frame to carve out the body. You can control the thickness nicely that way. I'd be more concerned that the workpiece would cup during carving so I would consider a vacuum table to control cupping until it is fully carved.

6. Your comment on the use of a bandsaw is standard with router use. Affix your template, use it as a guide for the bandsaw and without moving the template, move over to the router table. I might suggest that you make a table with two routers mounted and use one for the top pattern and the other for the bottom pattern.

Yes, you can use climb cuts but you're still working against the grain and you'll always have feathering when working against the grain. I still think your best bet is to flip the workpiece & pattern sandwich and always work with the grain.

I hope this helps. The world of routers is very confusing in part because of the versatility of the tool. But, a lot depends on personal preference and personal experiences.

HTH

 

Bearing-on-Pattern Flush Cutting

A couple of long-term considerations re: top (shaft end) versus bottom (cutter end) -affixed bearings:

1) Top-affixed can be extremely dangerous, hazardous to you, workpiece, etc., since you are committed to exposing 100% of the cutter length, whether hand-held or table-mounted. With bottom-affixed, you only expose as much of the cutter length as you need. Bottom-affixed flush cutters are safer and more versatile in my book; if I had to choose just one, I would always go with the bearing on the cutter end.

2) Top-affixed definitely have their place, though, particularly doing plunge cutting in addition to pattern matching. For example, if you have numerous portholes to cut into a boat hull, you will likely want a top-affixed bearing that will also allow you to plunge through the hull. Taking this example a step further, if there were insufficient space inside the hull for either the pattern or the router (and concavity!), you would be forced to pattern and rout from the outside the hull, and a top-affixed bearing would be a necessity, no choice there.

3) Good discussion about dual-bearings, climb-cutting, thanks all. Just a thought: if you get some 3M metallic tape, you can line your pattern with one or more layers of tape and do all your brutal cutting against the tape, carefully observing the aforementioned grain issues. I too prefer climb cutting, as tear-out on contrary grain can run deep, and flipping is not always feasible. Practice! Slip off the tape, wipe with solvent to remove adhesive residue, then make a light final pass, by now knowing all the nasty places on the workpiece very well.

4) Take you time, brace yourself for "grabbing," and most importantly, mind those fingers, **ESPECIALLY** with a top-affixed, 2" long, and table-mounted bit sticking 100% out of the bench.

 

Hi Richard:

Thanks for the comments. Your observations are indeed valid, however, I would like to proffer a rebuttal.

A couple of long-term considerations re: top (shaft end) versus bottom (cutter end) -affixed bearings:

1) Top-affixed can be extremely dangerous, hazardous to you, workpiece, etc., since you are committed to exposing 100% of the cutter length, whether hand-held or table-mounted. With bottom-affixed, you only expose as much of the cutter length as you need. Bottom-affixed flush cutters are safer and more versatile in my book; if I had to choose just one, I would always go with the bearing on the cutter end.

All router bits are dangerous and the same precautions should be taken anytime there is a bit in a router. A bit is dangerous even when the machine is unplugged. Anytime you use a router bit follow all of the manufacturer's warnings and instructions. Especially, watch the RouterWorkshop videos and familiarize yourself with the operation you want to perform before trying it yourself.

At this point, I have to be specific, I'm talking about a table-mounted router with a bearing'd bit used with a template. The reason I refer to the Router Workshop, above, is that they use a "safety pin" a.k.a. "starter pin." This little device is absolutely mandatory when using any bearing'd bit when you're not using a fence. Failure to do so and you get "grabbing" as you refer to below. You can also get your workpiece launched and your hand pulled into the bit.

There must always be three points of control when using a router. In this instance, the safety pin is one point, the table surface is the next and the bearing is the other point. Every time I setup the router, I count the contact points to be sure I'm not setting up a disaster.

3) Good discussion about dual-bearings, climb-cutting, thanks all. Just a thought: if you get some 3M metallic tape, you can line your pattern with one or more layers of tape and do all your brutal cutting against the tape, carefully observing the aforementioned grain issues. I too prefer climb cutting, as tear-out on contrary grain can run deep, and flipping is not always feasible. Practice! Slip off the tape, wipe with solvent to remove adhesive residue, then make a light final pass, by now knowing all the nasty places on the workpiece very well.

I'm not in favour of putting tape on a template. It usually takes me a lot more time to make the pattern and then the template than it takes the make the final product. When I make the template, I want it to have the exact dimensions that I need in the final product. I don't want to have to reconsider my dimensions. Also a tape will introduce errors itself. Especially where the tape may be applied less than perfectly.

4) Take you time, brace yourself for "grabbing," and most importantly, mind those fingers, **ESPECIALLY** with a top-affixed, 2" long, and table-mounted bit sticking 100% out of the bench.

I second your concerns for safety but rather than condemn working with an open bit, which I do routinely, I have to refer to the Router Workshop and their use of a safety pin. Plus, never start the router without three points of contact.

I respect your position and your objective but I don't have to agree with them. That said, the greatest benefactor of this discussion are those people who read the threads but do not participate. Thank you for taking the time to think through your points and presenting them clearly and eloquently. I would welcome other participant's take on this post. I love being wrong.

 

Hmm.. I can't really see why using the router on top in stead of under the table should be very different?