Tip Speed - a discussion

[Matt@Nearfield]

Maybe an old topic, but certainly an interesting one.

On another thread I stated that I prefer to use a VFD with a vfd rated motor as I feel it allows me to ramp up the speed the saw tips are moving which I feel gives me a better cut.

Studies have been done to determine the optimum tip speed for cutting hardwoods, softwoods, mdf, mfc etc.

Obviously the speed you pass the material through the cutting teeth will play a part in this... pushing the material through at one speed or another will make a difference.

Also, most saws have a nominal recommended sized blade, but also have a 'range'. I've always though this was a riving knife thing. For exam[ple, my Wadkin I'm curently working on is a BGS 12.. so a 12in blade. but can take a 14in, but also anything smaller.

Perhaps we could touch on the benefits of running a smaller blade (I actually prefer a 10in in many ways) .. for me it's cheaper and quieter.

Now the contention seems to lie in the fact that I prefer to have a slightly higher than the manufactures arbour speed and this is aparantly completely wrong. But after many years and many saws I've found a higher tip speed gives me a better cut.

Is this because I mainly bash out 18 or 22mm mdf sheet to make cabinets. I appreciate theres a loss of torqe, but I never run 3in hardwoods though the saw so not a real concern.

Is this because of the speed I push the materia through the blade?

Is it because the manufacturers tried to come up with a best compromise that will suit every potential use rather than end user specific (I expect so). Like a 2ltr engine for a 4x4 vs a sports car?

Is it becuase I prefer to use the much smaller gulleted teeth of PCD blades for the man made composite wood products I use?

I'm sure that math will come into this, so a few numbers:

Wadkin BGS 12 - 12in blade, arbour speed 3200rpm
Wadkin PK - 18in blade, arbour speed 3000rpm.

Just interested in other peoples opinions?

I've made popcorn..

M.

 

[Matt@Nearfield]

Just throwing some numbers into a calculator:

Wadkin PK 18in at 3000rpm give a rim speed of 72m/s - oem

Wadking BGS12 at 3200rpm gives a rim speed of 51m/s - oem

Wadkin BGS at 4500rpm gives a rim speed of 72m/s - pimped to70hz

 

[johnnyb]

interesting I've just fitted a video to a sedgwick morticer. it was set to 50hz max. how do you overspeed them. I guess it's some internal menus or some such.

 

[Matt@Nearfield]

Not sure why you'd want to. But but the best breakdown on VDF settings I've seen is a Playlist by Clough42 (I think) on you tube.. he runs through mist parameters. HTH. M.

 

[Inspector]

Where you are going is what in metal machining are feeds and speeds. For any given material and tool there is an optimum setting to get the maximum material removal rate or maximum tool life. Woodworking saw blade manufactures may also have similar information for any given blade and material combination but I was never in that field so can't say. I would expect if you contacted a saw blade manufacturer they could tell you what the optimum speed for their blade and rate of feed speed for MDF is. They would also have similar for other materials.

Poking around a touch I found a chart of recommendations but it doesn't cover manmade materials.

https://www.bendigosaw.com.au/page/34/what-speed-should-my-saw-blade-spin-at-
Pete

 

[Matt@Nearfield]

Great post buddy.

 

[Inspector]

Great post buddy.

Would you expect anything less from me??

Pete

 

[Matt@Nearfield]

Would you expect anything less from me??

Pete

You've set a level of expectation now though...

 

[ajs]

It's something I've thought about before and never really come to a satisfactory conclusion. I've mentioned here many times I drill a lot of printed circuit boards using tiny drills. The pillar drill I use for those is fairly fast by most standards - up to 8500 RPM, which makes sense when the typical hole is under 1mm. I'll generally use it at top speed with those drills and it goes through epoxy fibreglass like a hot knife through butter. Resulting holes are incredibly cleanly cut too. This fits with the cutting speed theory, after all linear speed is directly proportional to diameter and when drill (or cutting) most of the action is at the periphery of the tool.

On the other hand some components have larger leads, may need holes in the 1.2-1.5mm range. There I find I get cleaner holes backing off the speed slightly. Other parts are mostly mounted for mechanical support - heatsinks would be a common example. They may be 2 or 2.5mm diameter. I back off the speed to the minimum in top gear for those.

In general I do the same for the 4mm mounting holes too, although to be honest you get a better finish swapping the belt over to a lower gear I generally can't be bothered. It'll go through the board just fine at top speed/top gear, but the resulting hole is incredibly ragged with lots of exposed fibres visible. I've never understood why that is - after all a higher speed would rationally mean smaller bites are being taking by each tooth given the same feed rate. Can't be melting - after all epoxy is thermosetting and the glass - well forget it. Nor can I see the tool overheating in the space of going through 1.6mm of board in a second or less.

In summary... I've no idea.

 

[Fergie 307]

There is plenty of info out there on drilling speeds, but mostly for metals. Just a question of seeing where the fibreboard material fits in the scheme of things. I dont drill this much, but when i have I have used the speeds associated with aluminium with good results. But whatever the preferred rate for the tool it will always follow that the smaller the drill, the higher the speed should be.

 

[Goldfinger234]

I suppose to an extent, if you run a tablesaw with a 2” diameter smaller blade, then up the arbor speed effectively to compensate, you might as well just run a 12” blade. It’s the circumferential speed we’re talking about.

You shouldn’t harm the motor, nor the VFD. Changing the frequency is easily done via the VFD’s parameters. Power output will be lower, feed rate is important, as is the condition of the blade. Personally I’d be inclined to leave the speed as it is and invest in a quality blade for the particular material your cutting.

At increased frequencies you won’t want to put anything too thick and dense through the saw as the torque drops off above 50Hz irrespective of increased speed. If the reply is I’m cutting sheet goods, just get the right blade and keep it sharp.

 

[Fergie 307]

Maybe an old topic, but certainly an interesting one.

On another thread I stated that I prefer to use a VFD with a vfd rated motor as I feel it allows me to ramp up the speed the saw tips are moving which I feel gives me a better cut.

Studies have been done to determine the optimum tip speed for cutting hardwoods, softwoods, mdf, mfc etc.

Obviously the speed you pass the material through the cutting teeth will play a part in this... pushing the material through at one speed or another will make a difference.

Also, most saws have a nominal recommended sized blade, but also have a 'range'. I've always though this was a riving knife thing. For exam[ple, my Wadkin I'm curently working on is a BGS 12.. so a 12in blade. but can take a 14in, but also anything smaller.

Perhaps we could touch on the benefits of running a smaller blade (I actually prefer a 10in in many ways) .. for me it's cheaper and quieter.

Now the contention seems to lie in the fact that I prefer to have a slightly higher than the manufactures arbour speed and this is aparantly completely wrong. But after many years and many saws I've found a higher tip speed gives me a better cut.

Is this because I mainly bash out 18 or 22mm mdf sheet to make cabinets. I appreciate theres a loss of torqe, but I never run 3in hardwoods though the saw so not a real concern.

Is this because of the speed I push the materia through the blade?

Is it because the manufacturers tried to come up with a best compromise that will suit every potential use rather than end user specific (I expect so). Like a 2ltr engine for a 4x4 vs a sports car?

Is it becuase I prefer to use the much smaller gulleted teeth of PCD blades for the man made composite wood products I use?

I'm sure that math will come into this, so a few numbers:

Wadkin BGS 12 - 12in blade, arbour speed 3200rpm
Wadkin PK - 18in blade, arbour speed 3000rpm.

Just interested in other peoples opinions?

I've made popcorn..

M.

It is an intetesting subject. My experience has been that the choice of blade, number of teeth and tooth profile, and feed rate is the more important factor in dealing with different materials. Whilst I agree that theoretically blade speed could be changed as well, most saws dont have this facility, which they presumably would if it was felt to be important. Not sure the analogy with speeds and feeds in metals entirely works. If you look at the differences between machining say stainless versus aluminium, you are going to have all sorts of issues that aren't going to be relevant in cutting different species of wood. Think about a bandsaw and you have a similar situation, do you change the speed to cut different materials, or the blade?

 

[Matt@Nearfield]

Interesting.. u chance the freedom on my routers, Drills, sNders, jigsaw and table saw and spindle... as well as the planer speeds all the time. I also change out the tooling.

I think people have just not used to 7ding a single speed on a table saw which most saws don't accommodate as it not... well.. absolutely necessary. But VFDs are cheap now.

 

[ChaiLatte]

interesting I've just fitted a video to a sedgwick morticer.

VHS or Betamax?

 

[clogs]

is it all worth it......
not like a saw mill where ur cuttingmiles of the stuff......
now 74 and quite happy with the norm manuf speed....never needed more.....

bit like Jeremy Clarckson......SPEED.....

 

[Goldfinger234]

It is an intetesting subject. My experience has been that the choice of blade, number of teeth and tooth profile, and feed rate is the more important factor in dealing with different materials. Whilst I agree that theoretically blade speed could be changed as well, most saws dont have this facility, which they presumably would if it was felt to be important. Not sure the analogy with speeds and feeds in metals entirely works. If you look at the differences between machining say stainless versus aluminium, you are going to have all sorts of issues that aren't going to be relevant in cutting different species of wood. Think about a bandsaw and you have a similar situation, do you change the speed to cut different materials, or the blade?

Table saws are as old as the hills. I’m pretty sure, like you say, if the manufacturers thought several hundred extra RPM at the tip was going to make such a difference, they’d just increase the size of the arbor pulley, which wouldn’t be by much, and bingo, you’d have your extra speed with no money wasted on VFD’s. None of them do, and that’s pretty much all you need to know.