Circular saw guys

[Percy]

Today a guy older than me(really old) but seemed rather smart and not pushy or anything. I showed him my slabulator and demoed a slab being cut. As soon as he heard the saw cutting(cross cut), he said "The saw isnt spining fast enough" I hadnt considered that when I built the thing. POwer was and still is my primary concern. I figure I got it spinning around 2200 rpm. The stamp on the saw says 3780 max RPM. Its 30 inch carbide cross cut saw. teeth are left right  center(angles) and a tooth mabey every inch and a half. Is he accurate in his diagnosis? I hadn't considered tooth speed was important on an application such as this....Almost 70 and still learning...???
Thanks in advance....

[doc henderson]

It is hard to tell in the video as is looks to be barely turning at times, because I assume the video frame timing.  like a prop looking like it is turning backwards on a plane.  I guess the big thing is it can power through anything you may want to cut up.  It sounds like it pulls down some.  It has torque, and if you geared it up to a faster rpm, it would have less power to keep going, although the head start rpms may help.  this is where the flywheel debate comes in. good for a brief hard cut and then can recoup the rotational speed and momentum.

[doc henderson]

Many of the big processors drop down speed a bit as they try to cut/chop stuff as fast as possible.

[DanielW]

The 17,200 FPM rim speed you have now (assuming your 2200 RPM is correct) doesn't sound too bad for a 30" saw. I might have even thought it a little fast myself. But you say, "I figure I got it spinning around 2200 RPM". Where does the 'figuring' come in. Are you sure it's at 2200? Is your VFD still bogging down when it first enters the cut? 7.5 HP isn't a ton for a 30" saw, but if only cutting thin slabs, it would probably be ok. But if the VFD is varying significantly from 60 Hz. to get the RPM you need, then you have to worry about torque/HP concerns (depending on whether you're running faster or slower than 60 Hz.). I might start with (carefully) putting a tach on it while you enter a cut to verify what RPM it's actually bogging down to (assuming your VFD doesn't give a read-out for this).

[Percy]

The 17,200 FPM rim speed you have now (assuming your 2200 RPM is correct) doesn't sound too bad for a 30" saw. I might have even thought it a little fast myself. But you say, "I figure I got it spinning around 2200 RPM". Where does the 'figuring' come in. Are you sure it's at 2200? Is your VFD still bogging down when it first enters the cut? 7.5 HP isn't a ton for a 30" saw, but if only cutting thin slabs, it would probably be ok. But if the VFD is varying significantly from 60 Hz. to get the RPM you need, then you have to worry about torque/HP concerns (depending on whether you're running faster or slower than 60 Hz.). I might start with (carefully) putting a tach on it while you enter a cut to verify what RPM it's actually bogging down to (assuming your VFD doesn't give a read-out for this).

I didn't do the math on the actual speed. Motor spinning at 2100 rpm thanks to VFD. 
Motor pulley is 7 inches. Intermediate and saw shaft pulleys are 6 inch. 

Your comment about 7.5 hp for a 30 inch saw is accurate I'm learning. Also My generator is at its limit for amp draw which is one of my problems im learning. I need to limp along  with this till I can afford to upgrade to a larger genset and a larger motor. Would a 10 hp be enough or go for a 15?

[doc henderson]

If it is working for you, why change it.  if you keep blowing breakers and or stalling the motor then you have your answer.  Is the pulley on the motor and blade the same size?  need to know the relative size to figure the final RPMs and then linear speed.

[Ron Wenrich]

Rule of thumb for edger saws is 5 hp per inch.  That's in an industrial setting.   If your slabs aren't too thick, then it works okay.  If they get to be a real lunker, then it'll probably stall out.

A cord saw or buzz saw has a 30" blade and runs at 1300 RPM.  That has a depth of cut of 12", but its run with a tractor PTO.  It works on the same principle as your slab saw - cross cutting, not ripping. 

I worked at a mill that had a swing saw for board trimming and cutting chunks that wouldn't fit in the chipper or had nails in it.  That saw didn't run all that fast.  We slowed down on the big chunks. 

[longtime lurker]

I watched the video a while ago and remember thinking it seemed slow but small screens and aging eyeballs... I figured it was better than anything I've ever built.

But from your description above... 30 inch saw, ATB teeth, one every inch and a half... I'd say borrow a different saw for about 5 minutes cuz you've got way too many teeth and the wrong tooth type to boot. What you're describing to me is a docking saw blade designed for squaring ends in sawn timber with a relatively fine cut. What you need is a firewood saw with about 12 square teeth. Cut quality is irrelevant for what you're doing and making those nice smooth cut edges robs so much power

I'm going to link to my saw suppliers firewood saw range... I'd be trying to borrow something similar (ask your saw doctor he'll know who's got one ) for a whole couple of cuts to test one and see if it makes any difference. Behind that maybe a little flywheel for some stored inertia... but first I'd try and reduce the hp requirement of the saw

https://www.bendigosaw.com.au/category/7-dry-firewood-processing?_ga=2.250626182.1869909466.1725744670-429003508.1725744670

[Bradm]

The Amish around here run similar blades of 30x80x.260"kerf running at 1800-2200 RPM (your numbers look to be about 2450 RPM) on both their swing type end trimmers and slab saws.  I would like to know how the old timer determined your rim speed was too low, losing speed in the cut is a power thing that shows as an RPM thing.

Also, if you increase the RPM of the saw, get the blade retensioned for the higher RPM.  I remember one place that had a 24" blade with a 6mm (.2362") kerf that was tensioned for 1800 but was running at 3000 RPM; it took a cut that was almost 1" wide and hooked the cut like a very dull chainsaw, not to mention the extremely loud singing the blade was doing.

[Percy]

I watched the video a while ago and remember thinking it seemed slow but small screens and aging eyeballs... I figured it was better than anything I've ever built.

But from your description above... 30 inch saw, ATB teeth, one every inch and a half... I'd say borrow a different saw for about 5 minutes cuz you've got way too many teeth and the wrong tooth type to boot. What you're describing to me is a docking saw blade designed for squaring ends in sawn timber with a relatively fine cut. What you need is a firewood saw with about 12 square teeth. Cut quality is irrelevant for what you're doing and making those nice smooth cut edges robs so much power

I'm going to link to my saw suppliers firewood saw range... I'd be trying to borrow something similar (ask your saw doctor he'll know who's got one ) for a whole couple of cuts to test one and see if it makes any difference. Behind that maybe a little flywheel for some stored inertia... but first I'd try and reduce the hp requirement of the saw

https://www.bendigosaw.com.au/category/7-dry-firewood-processing?_ga=2.250626182.1869909466.1725744670-429003508.1725744670

THanks for the input and the link to a proper buzz saw blade. I had forgotten how much difference  less teeth make for power requirments. Ima goof. Bought two blades the same...No wonder Im broke

[barbender]

Well yeah Percy, if you're gonna stock up on something make sure it's wrong!😂