Tachometer in a narrow space

[paulengr 44]

I've got a tight quarters problem to deal with. We have a ductile iron horizontal centrifugal casting machine equipped with a DC drive for controlling the centrifugal speed. Almost directly behind the motor is an air cylinder that centers the mold inside the machine. There is only about 1" of clearance between the back end of the motor (these are double ended "clam shell" style mill motors) and the cylinder. The drive is an old Reliance MaxPak series (MaxPak Plus I believe...they've been through multiple Maxpak generations over time). A sister machine has a tachometer mounted on the back that provides feedback to the drive. The only feedback on this machine is armature voltage. Speed control is much better with a real tach instead of faking it. Shaft speeds are around 600 RPM. I thought about buying a timing belt and mounting the tach off to one side, but the sheaves are either so fat that they won't fit in there or the belt speeds get to be obscenely high. Plus I'm a little concerned about belt life in a foundry so that leaves me with the options of a chain drive (same thickness problem, plus the added need for a guard for when it goes flying off), or a big fat open gear. Anyways the cylinder would have to be removed every time it becomes necessary to replace the chain/belt anyway since there's very little room to work with. Any ideas on how to stuff a tachometer in such a small spot? Is there something available that would work well here?

[Ken Moore 23]

How about installing the timing belt pulley, and then using a prox. switch to count the teeth. RedLion and others make stand alone devices that will count the pulses and convert to rpm. The more teeth per revolution, the better the resolution will be. I've used this with good success on similar applications. In one case, I took a standard timing belt pulley and machined it very thin, so that it would fit. Since you are not driving a belt, you do not need the guides on each side, and you can use a small dia. prox switch., one inch of clearance will more than enough. No need to change out the belt.

[milldrone 0]

paulengr, Because you are using a tachometer and not an encoder, positioning acuracy is not a concern. Perhaps a "O" ring drive would work. This material is fastened by a clip or there is a plug rivet style (bottom of picture). The rivet has a barb on both ends and you just push it into the hollow urethane tubing. The materal comes in 1/4 od to 3/4 od sizes. I have used this material in regular "V" belt sheaves and it works just fine. a pulley size up to 6 in od would be fine if your top speed is 600 rpm. There is also another product orange go 85 that is repairable by plastic welding (soldering iron and clamping fixture). The manfacturer of this particular brand is Fenner Manheim but there are others. fenner.jpg Edited 11 Aug 2007 by milldrone