QX - Routing with Guide Bushings


Built a template to guide plunge routing of mortises, a first for me. I had a set of Bosch guide bushings one of which had an OD of 5/16 and an ID of 17/64. As I was planning 1/4 inch wide mortises and had a 5/16 straight router bit, that's the bushing I built the template around.
Lots of fussing, measuring, calculating and squaring ensued, but I got it done. Clamped a board into the jig, inserted 1/4 inch bit in my Bosch 1615 router in the plunge base, rigged up the DC and off we go.
Jig base was 1/8 hardboard to minimize loss of plunge depth - bad idea, too flexible, allowed router to wobble a bit and felt like the guide was riding on the work a bit 'cause it extended maybe a scosch more than 1/8 below the base. Ran first cut anyway (1 1/2 inch long, about 1/8 deep), brought the router back, plunged another 1/4, started the cut, and the bit contacted the inside of the bushing! In a flash the neat little peened over end of the guide bushing was gone and the guide was loose in the bushing plate. OOPS! I could't have drilled that guide out as cleanly or nearly as fast!
Question is, how much clearance does one allow between the inside of the bushing and the bit? Apparently 1/128 isn't enough, especially if things are going to wobble. I did not expect a 1/4 bit to deflect anything like 1/128, especially as I was just playing in Poplar end grain, not Bubinga or something tough.
And yes, the bit was properly tightened down and the guide bushing was locked in with that fancy Bosch spring loaded lock. If it matters, the bit was a relative no-name cheapy, 1/4 X 1 on a 1/4 inch shaft, but what it cut, it cut cleanly.
Any thoughts appreciated, I'm trying to learn.
Merry Christmas to all and all the best for the New Year.
Tom
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Tom Banes (in snipped-for-privacy@4ax.com) said:
| Question is, how much clearance does one allow between the inside of | the bushing and the bit?
At the risk of being obvious, enough to ensure lack of contact and to avoid any kind of debris jamming between the two parts. I'd go for an 1/8" or so.
Glad you weren't hurt.
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto/solar.html
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wrote:

While 1/128 seems pretty small, 1/8 seems awfully big for clearance between the bit and inside of the bushing. That would imply approximately 1/4" or so adjustment on the template to allow for the bushing plus bit clearance. This would also preclude the ability to use anything in a 1/4" bushing. I'm surprised the manuals don't address this. Would suspect 1/32 to 1/16 would be about the expected clearance requirement.
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Mark & Juanita (in snipped-for-privacy@4ax.com) said:
| On Sat, 24 Dec 2005 17:20:44 -0600, "Morris Dovey"
| || Tom Banes (in snipped-for-privacy@4ax.com) said: || ||| Question is, how much clearance does one allow between the inside ||| of the bushing and the bit? || || At the risk of being obvious, enough to ensure lack of contact and || to avoid any kind of debris jamming between the two parts. I'd go || for an 1/8" or so. | | While 1/128 seems pretty small, 1/8 seems awfully big for | clearance between the bit and inside of the bushing. That would | imply approximately 1/4" or so adjustment on the template to allow | for the bushing plus bit clearance. This would also preclude the | ability to use anything in a 1/4" bushing. I'm surprised the | manuals don't address this. Would suspect 1/32 to 1/16 would be | about the expected clearance requirement.
Could be - I don't recall ever seeing any guidance in any of the stuff I've read. I don't think I'd have any qualms about running a 1/8" bit in a 1/4" bushing; but I'll admit that I haven't used bushings for a very long time. I think the bushing that came with my old dovetail jig was 5/8" - I'll check it on Monday.
I think solid support for the router is considerably more important (and lack of same may have played a part in the OP's difficulties). If the bushing is well-centered and the router and workpiece are well-supported, then use of a larger than minimum bushing shouldn't have any effect at all on the operation.
It could be that I get carried away with my preference for keeping everything as far away as possible from whirly-sharp things. :-)
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto/solar.html
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I have never really thought about a minimum clearance, but I never would have tried 1/128. I suppose I might consider a 1/16, but an 1/8th or more would be closer to usual.
I do not know Bosch bushings, I thought they were all bolt in. I much prefer Porter Cable two part screw together. I am punchy about them coming unscrewed and tighten the tar out of them. I would be scared to death to hope I would feel an 1/8" stick out on the bushing to say nothing of a splinter or some such destroying my real piece. Enough stuff can go wrong with a 1/2" guide bushing exposed. I am just now starting to use a plunge router and still get out the B100 and 690's most of the time. I had one Bosch router and gave it away. They make a really fine electric jack hammer and a great jig saw. The rest of their stuff is not for me.
(top posted for your convenience) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

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A big part of my business runs on guide bushings. I have a bezillion templates for making cut-outs for undermount sinks for solid surface countertops. A 1/2' bit in a 3/4" OD bushing. That gives me an 1/8' minus the bushing-wall thickness. A sturdy brass one still leaves me a 1/16". Anything less than 1/16' would give me the willies. Because I use a single flute bit, most of the time, chip-clearance can be an issue but acrylic is fluffy stuff, jamming doesn't happen easily. Wood, like oak (that splintery crap) would be more of a concern, at which point I'd like 1/8".
A 1/128 certainly isn't enough as the bit never centres in the hole perfectly, especially in Bosch routers. (There are others which suck at being accurate that way, which is why in most cases, I end up making my own bases.)
Glad you weren't hurt or ruined a nice piece of work.
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... snip

Any guidance or pictures of any of the bases you've made? I'd be particularly interested in seeing how you have accomodated guide bushings in such bases. I'm getting ready to do a bunch of drawers and need to get an improvement to the Bosch's current >1/32" off-center problem.
Merry Christmas by the way.
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Pick up a Bosch centering cone...they run under $10 and will give a little insurance that the bit will be centered in the base. --dave
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I've got a centering bit, that's what is showing me that the base is offset.
I've found no way to adjust the router, so today I made my own base using 1/4" melamine board. 1. I first carefully drilled holes to match the existing base, 2. then placed the new base on the router and used the point on the centering bit to mark where the center of the router bit will be. 3. Drilled a small pilot hole through the reference point to allow reference to multiple bit widths 4. Used forstner bits to accomodate a PC guide bushing, both drilling a base recess for the bottom of the bushing, 5. then a smaller diameter hole through the rest of the base. 6. Used the centering bit to assure that the base was truly centered when the base was attached to the router.
I used it this afternoon with the Leigh jig. Got much better results than I had been getting previously.
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Thank you.
I will put together a little something with pics on how I made the bases I use. Gimme a bit of time as I'm up to my eyeballs in alligators till end of Jan.
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... snip

Thanks, I'll look forward to seeing that.
Good luck with the alligators, know how that goes.
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First, your bit would expand with heat before it even began to wobble, so you were dancin' with the Devil on that. The boys up in Manitoba use 1/16, and I've found that adequate for my shop.
If you can catch a few episodes of The Router Workshop, you'll learn that you don't need to measure and fiddle a bunch. Use a collar which will allow a bit as large as your mortising bushing to establish the distance between tacked-on pieces of scrap, nailed round and round, then plunge to make the template. For example, if you're going to do 3/8, you need a guide and a 1/2" bit to make the fixture.
The old bird on TRW hates to measure anything, and I can't say I blame him. When he does, he uses the layout bars, which, of course you could use instead of the bushing to establish the distance between wood strips.
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George:
Thanks - opened my old eyes! I much prefer the lazy man's method as you describe.
"Beware the lazy man, he'll sit and think and find a better way, just to avoid having to work." Misquote from Robert Heinlen.
Regards.

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I'd really like to use my Bosch 1617 for template routing, but every time I've set it up, I chicken out when I see how the bushing moves in the holder. I see at least 1/64" of play and no way to eliminate it. I always end up using my PC7529. I expect I'll be sending Pat Warner a check for one of his sub bases very soon.
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Try some Lexan to make your own custom bases. I hardly ever put the originals on any more. Also stick with high quality routers. Makita can't be beat. Bugs
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On Sat, 24 Dec 2005 16:33:26 -0600, Tom Banes
Thanks to all for the advice. I obviously expected far less wobble/expansion/off-centeredness etc. than what I experienced. A lesson learned. 1/16 minimum clearance, and 1/8 is better. I guess the bushing I used was intended for 1/8 or smaller bits. Wonder why they spected it at 17/64 ID? Seems to invite a 1/4 bit, doesn't it?
I'm also glad, as one respondent noted, that this was a test in cheapy wood, not a piece I cared about. That I've learned - trial in trash, then adjust. DAMHIK.
Hope everyone had a Merry and will have a Happy.
Pretige Feestdagen, Bonne Annee, Happy Hanukah, Happy Kwanzah, Eid Mubarak, Joyous Solstice, etc.
Trying to be PC here (afraid I've forgotten how to spell in Dutch, tho' can still speak it).
Regards.
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Measure it and you will find out.

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Tom Banes wrote:

Sorry to resurrect a thread that's been dead a couple weeks, but I'm still playing catchup. To show you that you aren't the only one that has done this, I figured a repost of my experience might be appreciated:
One of my scarier 'color me dumb' moments was using a brass template guide on my router for the first time. Pretty, shiny new 4" long, 1/2" Whiteside spiral upcut bit, and I picked the 5/8" guide... the one with a 17/32" ID. Hindsight tells me that only leaves 1/64" clearance all around the bit.
Now, the moment itself is a bit of a blur, but what I think happened is that the upcut bit, true to its name, lifted a freshly routed and liberated chip of wood that happened to be more than 1/64" thick. Said chip of wood (part of a knot in some pine IIRC) was thick enough to deflect the bit into the template guide, at which time there was an awful CHUNK sound, my router motor briefly stopped whizzing around and jerked violently in my hands, bits of wood, brass and carbide hit my face shield, and my heart stopped. Obviously, none of that is necessarily in chronological order.
Thankfully, the router, the bit and myself survived (mostly). The bit has a tiny nick on only one of its helical edges, so it still works great. The brass template... not so much. You can still sorta tell that it once had a round opening, but about 1/3 of it looks like it was torn and peeled back much like a cereal box top. The end grain of the wood I was routing got a little torn up, and needed nothing more than the tiniest dab of wood filler to fix. It is now the shorter stile in my first full-size door, and would make a great conversation piece if I didn't have to crowd people around it when I tell the story... it is a bathroom door.
-John
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