Speed up planer cutterblock with smaller pulley?

[LancsRick]

Afternoon all. Drive system question for an old Cooksley BPL planer/thicknesser. There is next to no documentation on these online, but you can find manuals for the BPJ which isn't a million miles away.

So, at some point in the past the machine was converted from a 2 motor system (independent feed and cutter) to a single motor. Through a pulley system this single motor drives both feed and cutters, but at a fixed ratio. Whilst the feed speed is good, I find the cutter speed to be slow (both by calculation and by sound/cut).

A quick bit of measuring and maths has got me to the point that I have a 1440rpm motor, with a 180mm diameter master pulley driving a 90mm diameter cutterblock pulley, giving me a cutterblock rpm of approx 2800. I can't change the motor RPM without changing the entire belt drive system to avoid speeding up the feed too, so my current thinking is taking the 90mm cutterblock pulley off and replacing with a smaller one (60mm potentially, need to check the minimum bend radius of the belt).

Any experience or issues with this approach?

 

[Trevanion]

How large in diameter is the cutterblock itself?

 

[LancsRick]

100mm

 

[Trevanion]

That is a little bit too slow then! :lol:

I only asked because these old machines can sometimes have horrendously large blocks. In an ideal world, you'd want it to be rotating at around 4800RPM or so at 4" in diameter but I guess you already figured that out.

A problem you may encounter with having a smaller diameter pulley on the cutter block is that you will lose power and there will be more of a chance for slippage. If it were me, I would be having a new stepped motor pulley made with the perfect diameter for the cutter block and the perfect feed rate to achieve 16-20 cutter marks per inch to avoid excessive knife wear and friction whilst also gaining the near best-finished surface you can. Do it right, do it once kind of thing.

Although bunging a 60mm pulley on the cutter block would be the cheapest and simplest solution.

 

[LancsRick]

I understand the chance of slippage, but why would I lose power?

I might see how much a 60 pulley will cost and give it a bash if it's cheap, and fork out for a full pulley if that doesn't work.

 

[LancsRick]

Of course the other option is changing one of the motor pulleys to a larger one assuming it will clear.... That might be the better option!

 

[Myfordman]

Consider using a cogged V belt as this will offer greater grip from the reduced wrap angle of a smaller pulley.

 

[LancsRick]

Great idea, thanks

 

[Argus]

A nominal 1400 RPM indicates a 4-pole motor running at 50 hz.
If you can obtain (or re-wire it) a suitable 2-pole motor of sufficient power, the resultant speed will be about double.... in the order of 2800RPM.
A trade-off in increasing speed via pulleys is may see a slight of reduction of power at the driven end.

 

[LancsRick]

The issue then is I will double my feed speed which I don't want.

 

[Trevanion]

I understand the chance of slippage, but why would I lose power?

It's only pulley mechanics, actual power loss would probably be negligible.

 

[Vann]

What's the design of the cutterblock? If it's a clamshell type - gripping the knives by friction only - you might want to be careful speeding it up that much (increasing centrifugal forces).
What you get away with at 2800rpm might go flying at 4800rpm.

I guess it shouldn't be a problem if all is in good nick and correctly torqued.

Cheers, Vann.

 

[LancsRick]

Clamshell?

 

[Trevanion]

A clamshell type head as Vann describes is a cutter block that has "clamshells" bolted to it to hold the knives in place, the clamshells enabled a degree of chip limitation by making the block circular in shape and to be able to use thinner knives than in the past since the clamshell would support the back of the knife. It's the successor to the old square head where the thicker knives were bolted straight to the head and it's the predecessor to gib type heads that are much more common today. I doubt that is what your machine has though, usually these heads are larger in diameter than 4".

Wallace is working on a Wadkin RB surface planer with this type of cutter head if you want to see one more plainly in a photo: https://www.ukworkshop.co.uk/forums/wadkin-rb-resoration-t122870.html

 

[LancsRick]

Nah mine has fixed slots with wedges that screw down into it

 

[Inspector]

How hard would it be to put a two motor setup back on? Did they butcher all the mounts and lugs? You could then fit any pulley combination you liked for the cutter head and with a variable speed motor adjust the feed to suit the job at hand or even on the fly when working with wood with occasional gnarly grain. Admittedly a little more money than a pulley or two. :wink:

Pete

 

[LancsRick]

I absolutely could, but as you say, pennies. I'll decide what I need and cost it up and go from there. If I have to start messing with scaling up the larger pulleys instead and I'm dropping 100 quid all of a sudden then I might consider a motor at that point.

 

[no idea]

Is slowing the feed speed down instead an option?

 

[Trevanion]

Is slowing the feed speed down instead an option?

Why have a lame and swaybacked donkey with three legs?