another router (trimmer) question. bit speed

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another router (trimmer) question. bit speed

Postby Simon Magennis » Tue Jan 30, 2018 11:31 am

Reminder … I'm a router newbie.

I got myself a 1/4" flush trim bit with a 1/4" shank for my Bosch GFK600 mentioned in this thread. (viewtopic.php?f=12&t=5392)

The Bosch is fixed speed 33,000. On the shank of the bit it says "n max 24,000" - there is no n-max mentioned in the description on the sellers website as far as I can see but of course I might have overlooked it.

It is clear that if a commercial enterprise put the two items together in the UK, the health and safety authorities would not be happy. The purpose of the bit is to trim the edges of the top and back of classical guitars prior to routing out the binding channels so not a heavy load if that matters in the least.

Would you use it or not?

I will have to look up the speed for the cutter I have been using for the bindings. Never gave the speed a second thought.
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Re: another router (trimmer) question. bit speed

Postby Barry Daniels » Tue Jan 30, 2018 11:59 am

I wouldn't worry about it. Just keep in mind that 1/4" shank bits are not meant for heavy stock removal. Take small bites and don't advance the bit more than 1/8" a pass.
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Re: another router (trimmer) question. bit speed

Postby Clay Schaeffer » Tue Jan 30, 2018 1:54 pm

Assuming it is a carbide bit, I would look at how well the carbide is brazed to the steel shank. My guess is that if it is going to fail that is where it will fail. It is kind of a general rule to rate bits under an inch in diameter at 24000 rpm or less. As the size of the bit goes up the "or less" rating goes up - larger bits should be run slower. The "no load" speed rating is generally more than the speed a small trim router will spin at under load.
If it is not a cheap poorly made bit and is of small diameter, I don't pay much attention to the rated speed, but perhaps I'm being foolish.

1/4 inch flush trim bits are usually of two types - those with a tiny bearing, and those called "self pilot" (either solid carbide or HSS) I don't like either. The tiny bearings on the carbide tipped bearing type tend to gum up or burn out and fly off. The self pilot type fall into every nook and cranny and heat up as they "rub" along and burn the material they are pressed against (which the bearing type will also do when it locks up) leaving an indented burn mark that needs to be sanded out.
I much prefer the 1/4 inch shank / 1/2 inch flush cut bit with a bearing (and keep it oiled and spinning free) that is large enough to hold up.
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Re: another router (trimmer) question. bit speed

Postby Simon Magennis » Tue Jan 30, 2018 4:02 pm

Thanks indeed for the responses. Kind of inline with my own gut feelings. So long as the load is low it shouldn't be significant. I emailed the place I bought it from and they told me that the put the same bit into a kit with the GFK600 so they reckon it is just fine despite the printed listing.

@ Clay …

What kind of oil do you recommend for this kind of usage. I have become more oil aware over the last few years when I discovered the "magic" the right oil can do.
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Re: another router (trimmer) question. bit speed

Postby Barry Daniels » Tue Jan 30, 2018 8:15 pm

You should use a thin oil meant for high speed rotation. Most grease is too thick and gummy to be spinning at 25k rpm. I use Speed Oil that I got at a skate board shop.
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Re: another router (trimmer) question. bit speed

Postby Christ Kacoyannakis » Wed Jan 31, 2018 7:35 am

I think there is a general rule that you should not try to route more than 1/2 the width of the bit. So, if it is a one inch wide bit, you should only try to route 1/2 inch depth with each pass. Seems to work better and faster the shallower cut you take, plus easier to control the router.
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Re: another router (trimmer) question. bit speed

Postby Barry Daniels » Wed Jan 31, 2018 11:15 am

Don't forget about depth of cut. I usually only go 1/8" deep for each pass. You can feel when you are pushing the limits of cut. Also, one of the most important factors is the diameter of the shank. Cutting half the width of the bit for a 1/2" shank bit is a lot more doable than doing that with a 1/4" shank bit.
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Re: another router (trimmer) question. bit speed

Postby Clay Schaeffer » Wed Jan 31, 2018 1:41 pm

When bits are new I think they have a grease (probably lithium grease) in the bearing race, but in time and use it is lost. Bostik makes an aerosol bearing lubricant, but I don't use it (too cheap!). I have used light weight oils (sewing machine oil) and even motor oil (5w30) for cleaning and lubing bearings. Once I start oiling them I oil them after every use.This seems to prolong their life. Once bearings start to feel "crunchy" when you spin them by hand it is time to replace them because they are getting ready to fly apart under load.
One "lubricant" I would avoid putting on bearings is WD40. It will remove any grease remaining in the race and dry it out. It really isn't a lubricant, but rather a solvent that evaporates into the ether, leaving little behind.
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Re: another router (trimmer) question. bit speed

Postby Simon Magennis » Thu Feb 01, 2018 7:41 pm

Clay Schaeffer wrote: ...
One "lubricant" I would avoid putting on bearings is WD40.


Thanks for that. That is something I might have grabbed. :-)

A now deceased, German maker, told me he used engine oil for lubricating tuners. Another make I know use bicycle chain oil as his go to oil. I recently got a bottle of a Japanese Camellia Oil. Not sure exactly what it is good for.
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Re: another router (trimmer) question. bit speed

Postby Barry Daniels » Thu Feb 01, 2018 10:18 pm

I think that is a rust preventative for chisels.
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