Replies

1. 
   KeithNewton | Feb 07, 2005 12:12pm | #1

   jack, you should check at the forest product lab in madison Wi.
   Other than that, there is good info in the Memphis Machine catalog.

2. 
   mvac | Feb 07, 2005 03:56pm | #2

   Jack,

   Would you mind posting the info when you get it? I'd be very interested in seeing it. Thanks, 

   Mitch

   "I'm always humbled by how much I DON'T know..."

3. 
   hammer1 | Feb 07, 2005 04:27pm | #3

   I often run large panel raising bits on my PC 7518 with the various speed options. I have tried all the different speeds as well as feed rates. Regardless of what all the experts say, I find that the bits chunk and kick at low speeds. The best option is always to take less of a cut and slow down the feed.

   There aren't many variable speed shapers, table saws or joiners out there. One piece of maple will not necessarily cut the same as another. I run my router full speed and adjust the feed rate and depth of cut accordingly. On lower speed, minimum cut and even a creeping feed rate I can stall my big PC. I think the reduced speed idea is put forth by those who don't actually do any cutting. It has never worked for me and it is more dangerous when it causes kicking. It seems to me, the bigger the wheel, the longer it takes to make a revolution, not the other way around.

   Beat it to fit / Paint it to match

1. 
   highfigh | Feb 07, 2005 05:02pm | #4

   Reducing the speed of a large router bit reduces the momentum of the bit. The large ones have a lot more momentum than small ones. Taking smaller cuts is a good idea, though because with the larger diameter, there is also more cutter in contact with the wood and the wood provides more resistance to the cutter's rotation. Going to lower RPM with large or aggressive bits is dangerous. As far as the bigger wheel taking more time for each revolution- on startup, yes. Once it gets going, 22,000 RPM is 22,000 RPM regardless of the cutter diameter. That's constant angular velocity(22K x 360 degrees/sec). However, the actual speed at the outer edge of a larger diameter bit is a lot faster.
   "I cut this piece four times and it's still too short."

2. 
   GHR | Feb 07, 2005 07:16pm | #5

   In general and with all other things being equal, you want the speed of a cutter, ft/min of the outside edge of the cutter, to be the same for a small diameter cutter or a large diameter cutter. This requires large diameter cutters to be run at slower RPM than small dimeter cutters.The fact that there are few variable speed shapers, tablesaws, or jointers indicates that diameter of the cutters for those machines do not change much.

4. 
   gizmo2006 | Feb 08, 2005 02:04am | #6

   Jack,

   Check out http://www.thewoodworkerschoice.com/saferouting.com. They have a chart that lists recomendations for router bits based on bit diameter and material being used.I've found that most companies list a maximum suggested RPM for each router bit they produce.

   Delbert

1. 
   forestgirl | Feb 09, 2005 07:51pm | #14

   The above link had a mistake in it.  Here's the URL:http://www.thewoodworkerschoice.com/saferouting.htmforestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the  "I Rocked With ToolDoc Club" .... :>) 

1. 
   gizmo2006 | Feb 10, 2005 04:06am | #16

   Thanks for catching the mistake. Sorry I made it.

   Delbert

1. 
   forestgirl | Feb 10, 2005 07:28pm | #20

   Hi Delbert, no apologies needed.  Thanks for posting the link, I bookmarked the chart -- much better than the others I've seen -- and it'll be a handy reference when rpm questions arise!

   I take the lazy way out on posting links:  copy/paste from the address bar, or "copy shortcut" from the right-click menu.  forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the  "I Rocked With ToolDoc Club" .... :>) 

5. 
   Midnight | Feb 08, 2005 04:53am | #7

   I;ve found the Freud catalogue is a good help when matching cutter diamater to router speed... canna say I've come across remommended feed rates though... If you find anything, I'd be interested in it too...

   Mike Wallace

   Stay safe....Have fun

1. 
   JackLindsey | Feb 08, 2005 10:16am | #8

   Thanks for the input. I'll check out the sites you have recommended.

2. 
   highfigh | Feb 08, 2005 05:46pm | #9

   How are you going to monitor the feed rate? That's something you already know how to change on the fly, right? I think we have all had situations where we went too fast and it grabbed or tore out and others where we fed it too slowly and it burned due to the high sugar content.
   "I cut this piece four times and it's still too short."

1. 
   mvac | Feb 09, 2005 05:11pm | #10

   I'm still trying to figure out whether what you said about router speeds was contradicted by what George said! I think it was - and if so, who's right?

   Regardless, I would highly value a recommended feed rate chart for certain woulds, bit diameters, etc. I'll ask around.Mitch

   "I'm always humbled by how much I DON'T know..."

1. 
   Manchild | Feb 09, 2005 05:28pm | #11

   I think George has a point. He just went too far slowing it down and his router doesn't have the power or momentum at the lower speeds.

   If you think about a shaper it has a big heavy motor with a big heavy shaft and cutter. Big routers have a HP rating that is high but there's no way they even come close.

2. 
   highfigh | Feb 09, 2005 06:16pm | #12

   I don't think he contradicted me. What I was getting at was that a larger bit, especially if there is more weight at the outside perimiter, will have a lot more momentum than a smaller diameter bit. However, if something tries to resist the bit's rotation, it's harder to slow a small diameter bit than a large one. Kind of like a car without power steering-it's easier to driver with a large dia steering wheel. Basically, if it's an agressive bit, don't try to remove everything with one pass, and if a chart is available, it's a good idea to use it. Slowing the router too much will result in chunking the wood out. I would like to see the router manufacturers come up with a way to actually know the RPM of the motor. I haven't had problems from the speed being too high but I've had some with it being too slow, however.
   "I cut this piece four times and it's still too short."

1. 
   CUEMASTER | Feb 09, 2005 07:39pm | #13

   highfigh;

   You ca use a cheap strobe light and a felt marker to check RPMs.Quick and safe as it's a no contact measure.Aftermarket tachometers which sense the commutator switching can be hooked into the motor wiring to give a contin,reading to quantify slow down at load and moniter feed rates,

   Art

3. 
   GHR | Feb 10, 2005 01:10am | #15

   I don't think I contradicted anyone.

1. 
   mvac | Feb 10, 2005 08:47am | #18

   George,

   "I don't think I contradicted anyone."

   That probably reflects the fact that the conversation was over my head. That said, it's not like I shot your dog... :-)Mitch

   "I'm always humbled by how much I DON'T know..."

6. 
   cowtown | Feb 10, 2005 04:36am | #17

   I dunno if many folks will agree with the perspective that follows, but to start with, I am sure that most folks will agree that machinists use substantially more consistant materials than is found in wood, and that there has been considerable effort, in fact whole manuals of cutting speed. Theres been a good hunnerd years of effort in achieving maximum efficiency on metal lathes, milling machines, etc etc,

   That being said, the tables I've read are prefaced with the caveat that these speeds are only intended as guidelines.

   So in wood, where yer sawblade may run from sap wood to knots on the same board, is there any liklihood that a recommended cutter speed is gonna do the trick?

   I got chastised when I posted this pragmatic observation on another forum, in relation to using my 8" dado blades on a 10" saw (My rim speed was obviously changed, so it was suggested that it wouldn't work correctly- when clearly it did...)

   Once you start listing variables starting from the HP driving the cutter, feed rates, hardness of material, variability of hardness of material, profile of cutter (big cutters got bigger load factors, slow down more with increasing feed rates) chip clearing ability of cutter (Poor chip clearance-->overheating, no cutting, burning) sharpness of cutter, it becomes clear(at least to me) that no one table is gonna give me any more precise "cutting data" than my own inate sense of what works and what isn't.

   To be sure there is a good deal of science in wood cutting, but there is also a not insignificant amout of art involved.

   Just my thoughts, however unpopular.

   Eric
   in Calgary

1. 
   mvac | Feb 10, 2005 08:49am | #19

   Eric,

   Thanks for bringing this discussion back to basics. Sometimes it comes down to feel and experience, experimentation and going with your gut. That's why we never order the exact amount of board feet for a job after all, isn't it?Mitch

   "I'm always humbled by how much I DON'T know..."

2. 
   GHR | Feb 10, 2005 11:26pm | #21

   I will agree with you.If you look at a good production shop, you should find that the machines are fine tuned for the work to be done.Small shops and home shops almost always use the wrong speed. It is simply not cost effective to find a better speed.

1. 
   highfigh | Feb 10, 2005 11:32pm | #22

   Unless the maching is already set up for multiple speeds, like a lot of bandsaws. To those of you with 8" table saws, what is the motor speed on your saws? Is it 3450RPM like a 10" or is it 5000RPM? I ask because of the 8" dado sets and whether they should be used on a 10" saw or not.
   "I cut this piece four times and it's still too short."

1. 
   cowtown | Feb 12, 2005 09:48am | #23

   you ask whether an 8" dado set should be used on a 10" table saw?do you have any indication that it shouldn't? Most small shops that I know of do it all the time.So do I.the difference in rim speed is only 20%, well within the variance which might be induced by worn pulleys, slipping belts, underpower or dull blades etc. I think in fact that the dull 10" saw blade drops the cutting efficiency by 40-50%, so a 20% difference is practically insignificant.It works, therefore it gets done. Canadian pragmatism at work I guess.Moreover, if anybody is really particular about the significance of that 20% drop in rim speed, all they have to do is drop their feed rate 20% and you got the same # of cuts per second. After all, we all scientifically measure our feed rates don't we? I admit to lapsing in that heuristic (black box) endeavour back about 30 years ago and haven't bothered since. The point is any shortcoming in quality of cut can be compensated with simply slowing down the feed rate 20% for the 15 seconds it takes to feed an 8' sheet through the table saw. You would waste about 3 seconds, but the world wouldn't end because of it. Besides, if yer cutting dados, you gotta hold yer work down on the table, so chances are you ain't even gonna notice the wasted three seconds a cut. Besides, my 10" dado set after years of work and many sharpening, needs retoothing. I cost me less to go to the highest end 8" dado set I could find than it was to retooth the 10" set. A simple economic lemma, ie a no-brainer.My residential, commercial and architectural clients never even noticed. I couldn't detect any difference in product appearance. Changed over 5 years ago, so I no longer hold my breath waiting for the axe to drop. It simply didn't.i guess I shold add that I use them zero clearance blade inserts all the time. That makes a difference in quality with any blade, big or small. What would you be cutting that is so persnickity or have you actually tried an 8" dado set on a 10" saw. So try that 8" dado set, and don't worry, be happy. Eric
   in Cowtown

1. 
   highfigh | Feb 12, 2005 02:11pm | #24

   My question was mainly rhetorical, actually. Most of the previous posts were about being very precise with feed rate and cutter speed, which are hard to monitor unless the motor is variable or a feeder is used. As you said and I do, slow the feed rate when the cutter speed is lower. I never force the stock through. If I'm in a hurry, I won't worry about making the cut. There's always tomorrow. I use zero clearance plates too although I need to make some for dado cutting. I have a Freud 8" dado set and it cuts very well, even though it was relatively inexpensive. Definitely not a great set but does what I need. I got it for cutting some melamine covered particle board and needed something with negative hook. I won't use this set for the same material again since the carbide was pretty well trashed when I was done. Most, if not all, of the tips were chipped. The guy at Rockler told me that it was due to all of the metal in the particle board and that I could have probably seen sparks had it been dark while I was cutting. I know particle board is like hot dogs in terms of its content, but in all of the years I have worked with wood, I have never seen teeth chipped the way they were. He told me that I shouldn't cut PB with the set I bought, even though the labels show that it's suitable. Nobody at the store knew what negative hook angle was, but he apparently knew that I shouldn't be cutting PB. Yeah?With a crosscutting blade, I have cut through 16d nails that I didn't know about and the blade was fine.
   "I cut this piece four times and it's still too short."

2. 
   GHR | Feb 12, 2005 05:32pm | #25

   I don't do a lot of different types of wood so ...When I decided my bandsaw was running too fast for the wood I was cutting, I changed pullies and reduced the speed by 10%.As I said before small shops almost always cut at the wrong speed.

3. 
   highfigh | Feb 12, 2005 08:32pm | #26

   What kind of wood was it? I assume it was really hard, right?
   "I cut this piece four times and it's still too short."