Airtool... how can I decrease RPM without decreasing torque?

[Dadnatron]

I have a project in which I need a 'die grinder' type device for power, but I don't want the RPM of a typical die grinder.

I am looking for something to power a cutter which I am designing, but need the RPM to be drastically lower. Tho RPM on the tools I have seen are in the range of 13-20K and I am looking for something in the 500-1000 or even less range. (At least at this time.) However, I still need to keep the torque of the machine to run the cutter. I am afraid, although I don't know for sure, that the high RPM will cause too much heat in the foam I am cutting. (memory foam type material)

I am not familiar with airtool workings. I have and use several, but that is it... I use them. The most I do to them is oil them.

I suspect there is a way to decrease the RPM via orifice reduction etc. But I also suspect that would drastically decrease the effective torque. Otherwise, I suspect I would need to change the internal 'gearing' in some manner, which I am willing to do, if it is reasonably accomplished by a 'novice'. I am pretty handy, and not afraid to take on a task, and I am willing to 'sacrifice' a few HF tools in order to give it a try. But, I don't know where I'd begin.

If you know of a die grinder/cut off tool with either a variable speed or MUCH lower RPM, that might work for me without necessitating all the hassle. I also don't know whether simply turning down the air pressure would decrease speed without torque, although I would think both would be affected.

Straight cutters, saws, hot wires, etc will not work.

I need to be able to slow down a cutoff wheel machine or something along those lines. Something similar to or along the lines of the pic below.

 

[4570Man]

Maybe use an air drill that already turns slower? I don’t know of any way to slow an air grinder without loosing toque short of an external gear box.

 

[bcp]

700 RPM, $26

1/2" Reversible Air Drill

Bruce

 

[Industrial Toys]

I have a large variable speed dremel. But, even variable speed (110V) electic tools lack power when you slow them down as there is not a feedback circuit.

 

[RNeumann]

700 RPM, $26

1/2" Reversible Air Drill

Bruce

I have a simple inline valve that allows for fine air flow adjustment. But it doesn’t really work well to adjust RPM- it seems to either spin or not spin as opposed to being variable speed.

My thought was exactly what is posted here- find a tool with the correct RPM.

FYI- I thought most foams were cut with an electric knife......like the old school knives you used to cut the turkey with.

 

[Dadnatron]

The drill might work... but my issue is the handle angle will get in the way of my cutter. If I rotate it out of the way, then my control on the cutter requires 2 hands which takes away usefulness. Otherwise, I could just use a cordless drill. But I wonder whether I could scavenge the guts of the drill and move the important parts to a die grinder or cut off. perhaps just the gearing etc.

I was reading and it appears there might be the possibility that a flow valve will decrease the RPM while maintaining torque. But I'm not sure. Any recommendations on good types of flow valves which maintain constant pressure?

Air Motor Selection and Sizing | Hydraulics & Pneumatics

• Air motor speed can be regulated through simple flow-control valves instead of expensive and complicated electronic speed controls.
• Air motor torque can be varied simply by regulating pressure.

 

[4570Man]

I doubt the drill has gearing except for the right angle gears. I imagine it’s a similar concept to a hydraulic motor where you use a bigger displacement motor in relation to the flow to go slower.

 

[bcp]

There are in-line air drills.

Here's the first I found. It costs a little more than the HF drill.

https://www.intlairtool.com/dotco-inline-drill-15lf085-40-0-4-hp-3-8-24-e-drill-diameter-capacity/

More:
In-Line Air Drills - Grainger Industrial Supply

Bruce

 

[aczlan]

The drill might work... but my issue is the handle angle will get in the way of my cutter. If I rotate it out of the way, then my control on the cutter requires 2 hands which takes away usefulness. Otherwise, I could just use a cordless drill. But I wonder whether I could scavenge the guts of the drill and move the important parts to a die grinder or cut off. perhaps just the gearing etc.

I was reading and it appears there might be the possibility that a flow valve will decrease the RPM while maintaining torque. But I'm not sure. Any recommendations on good types of flow valves which maintain constant pressure?

Air Motor Selection and Sizing | Hydraulics & Pneumatics

• Air motor speed can be regulated through simple flow-control valves instead of expensive and complicated electronic speed controls.
• Air motor torque can be varied simply by regulating pressure.

No load speed will be higher than loaded speed, but a simple valve inline will reduce loaded speed without reducing loaded torque.

Aaron Z

 

[BLSXJ]

in theory... you want a flow control valve... it limits the volume of air flowing without a pressure drop. I use them to control the speed of a pneumatic cylinder, without reducing force.

 

[4570Man]

in theory... you want a flow control valve... it limits the volume of air flowing without a pressure drop. I use them to control the speed of a pneumatic cylinder, without reducing force.

That’s different. Lots of people confuse volume and pressure with cylinders. Volume controls speed. Pressure controls force. A cylinder with a volume of 1 gallon per hour at 2000 psi would reach the same force as if it had 10 gpm at 2000 psi.

 

[ray66v]

You can't slow down a conventional pneumatic die grinder anywhere near that much, and have it be of any use to you. They only produce power at high RPM's

An industrial right angle pneumatic die grinder can be built to run slower, because they have gearing. They are still rated at around 9,000 rpm. It would probably run at about 7,000 rpm, with a load on it. Perhaps you could throttle it back as far as 5,000 rpm, and still have power. They are also expensive, $250-$400.

 

[Xfaxman]

Does it have to be an air tool?

A lot of different ways here: cutting memory foam - YouTube

The bandsaw worked well: Bandsaw Memory Foam Test Cut 1 | Forrest Manufacturing - YouTube

And the electric cutter: Acu-Cutter Foam Cutting Tool - YouTube

 

[CalG]

Get an air powered nut runner, or screw driver. They all have planetary gear reduction in an inline chassis.

Ingersol is one brand, Rockwell,...etc... there are many more.

 

[finn1]

Or, perhaps an air ratchet.

Air motors need gearing to produce torque at the output shaft.

The basic air motor is a high speed, low torque device.

 

[Fallon]

Does it have to be an air tool?

A lot of different ways here: cutting memory foam - YouTube

The bandsaw worked well: Bandsaw Memory Foam Test Cut 1 | Forrest Manufacturing - YouTube

And the electric cutter: Acu-Cutter Foam Cutting Tool - YouTube

Ya, air tools are very inefficient at transmitting power. Going with something electric might be better unless you need air powered for some specific reason.

 

[Dadnatron]

Ya, air tools are very inefficient at transmitting power. Going with something electric might be better unless you need air powered for some specific reason.

None of the other cutting methods will work for my needs. There is NOTHING out there, which will do what I need at this point, (at least that I have found over the last 3 years) therefore, I am designing and building it. However, my current need is a power source. Electric is fine, but it can't be very large, as the work will need to be done single handed and I think trying to manipulate a 'small grinder' sized power source with my cutting head attached would be too cumbersome. Therefore, I have been thinking of alternatives.

The 2 I've come up with so far:
1. Something like an air powered device in which the handle/motor is a small unit, which would allow me to grip and handle the power and cutter in a way which is more likely to work than an electric motor unit.
2. A Flex-shaft device of some sort in which I can attach the head to the shaft and use it in that manner.

Ultimately, if my project works out, I will finish my CNC design, but that is going to be real $$$ in both investment in Engineers as well as materials. I have to prove my product before I worry about how to produce it better.

I am making custom pillows for my patients with special requirements. They work... but I cannot realistically make them in the manner I have been... ie a kitchen carving knife.

 

[4570Man]

So I remember this thread before although I don’t remember the details. Did freezing the foam and using a regular CNC built for wood not work?

 

[Xfaxman]

Did you try a serrated electric kitchen knife?

It is hard to believe that with all of the electric upholstery foam cutting knives available, you didn't find one that would work: electric foam cutter - Google Search

 

[bigtiller]

I wonder what mike lindell uses to cut his foam.