Motor speed controller

Interesting. I did see a post a while ago about that same contact wheel from Grizzly but instead of machining it for bearings, he mounted it permanently on a shafts that ran through a pillow block.
 
I have seen people who have put bearings in the Grizzly wheels with good results; but the one I did would not run true. The first time I indicated the hell out of it and bored it in a mill with DRO, and the second time it was indicated and bored in a lathe with DRO. I think the rubber is just ground wrong on the one I got. A pillow block would work if you can stand the added weight to the tooling arm.
 
Go with an 8" wheel for the contact wheel. If you're trying to cheap out, use one of the Chinese VFD that sell for $116 (open enclosure works by putting a filter over intake) and buying a 2hp 3ph TEFC motor for $127 shipped. That's the route I went on my last grinder I built last year.

If you need more info, I can post links.

Ken H>
edit to add link: http://knifedogs.com/showthread.php?38839-New-Grinder-for-me
 
Last edited:
I think i'll go with the three step pullies and a pillow block with a long shaft to accomodate a disk sander on the side.
I saw a grinder a guy made with an assembly that had the 2 2" contact wheels and a platen on one side and could flip it over to use a contact wheel. He had made the whole unit from a treadmill and a bumper from a car. Was intresting to say the least.
Thanks all for all the amazing info. Now to find a knife maker in the area to yack with in person. ☺
 
OK that first design, It has 2, 6 inch wheels in the original plans. I saw someone on here suggest an 8 inch contact wheel. A guy on ebay in the US has a package with a 12 inch contact wheel. I'm a little confused what would be best. Early in my delving into knife making it seemed that bigger wheels were better ( I imagine to a point). The design im looking at above has the two 6 inch wheels, Would it be better to say put one 2x2 aluminium wheel up top and a 12 inch or an 8 inch on the bottom or use 2 8 inch wheels?
Also, I have decided to go with the pullies. Is there a formula to figure out pulley speeds and is there a maximum speed I should not go over? And an optimum speed?

The motor speed is 3450 RPM.
 
3450 (which is a 3600 RPM with "slip" already calculated in. Slip refers to the difference between the speed of the rotating field and the actual speed the rotor will turn. All induction motors slip, or else they wouldn't work)

Anyhoo- 3450 at the motor is your top speed. What you really want is the ability to slow down. Arrange your pulleys with that in mind.

Your drive wheel determines belt speed (linear speed, in feet / minute). A 3450 motor and a 4 inch drive wheel is standard for a belt grinder- plenty fast. (Too fast in the beginning.)

The size of the idlers is inconsequential to any of this. Size those based on what you are trying to accomplish grind-wise.

2inch idlers are great when used with a flat platen. 2in provides just the right radius to transition the belt on and off the platen without a big gap. 2inch is also super handy for handle shaping, sheath sanding, and finish grinding bottom curves of the tang. It's just a very useful radius.

8 or 10 inch wheels used alone are also extremely useful. I use my 10in wheel for every step of the process other than grinding bevels. (i flat grind). For instance, I find it is a lot easier to profile blanks on a contact wheel vs a platen. All of my rough handle shaping is done on a big wheel.

I don't know what I'd do with a 6in wheel but a 4in would be handy for handle shaping at times.

I could not live without:

8 or 10 in contact wheel (one or the other)
2 in wheel (already part of my platen)
Flat platen
1 in and 3/4 in in a small wheel attachment


Sent from my iPhone using Tapatalk
 
Last edited:
David Danek said:
....... or use 2 8 inch wheels?
Also, I have decided to go with the pullies. Is there a formula to figure out pulley speeds and is there a maximum speed I should not go over? And an optimum speed?The motor speed is 3450 RPM.
Click to expand...

I can't really see any advantage to using two 8" wheels. I sort of favor using a 2" at the top of the platen and a larger wheel on the bottom. As far as speed, I consider 3450 the top speed of my grinder, I almost never run my grinder that fast. On your pulleys, think of them as ratios. If you put a 4" pulley on the motor and turn an 8" pulley, you have a 1:2 ratio. So, 3450 would be slowed to 1750. turn a 10" pulley and you'd have a 1380 rpm.

My advice is to have at least a 3 pulley setup like the KMG. For the top end speed, have a set that are 1:1. The middle set should be 1:2. Then, maybe a 1:4 set for your slower speed. Study the KMG's out there, you can't go wrong if you copy them. That first design pic you had, might be hard to setup with multiple pulleys, so in that case, I think if I could just pick one ratio with your motor, I'd go 1:2 and keep the working rpm at 1725.

Disclaimer: I'm new too and I've only built one grinder, so I may have no idea what I'm talking about. :biggrin:
 
Awesome information.

Thanks for the reply. All the people on this forum are the most gratis with there wisdom of any forum I've belonged to. Thanks you all and Merry Christmas to all of you.
 
Tank you Anthony. Your willingness to share from your experience is much lyrics apreciated. You claim to be new. But I'm just starting out with nothing as far as experience goes.
 
The Chinese HuanYang controllers are able to output up to 400 Hz for use with high-speed spindle motors. I usually program them for a maximum frequency of 120 Hz when using them with standard industrial 4-pole motors to give double the 60 Hz mains speed, which is the same as the 60 Hz mains speed of a 2-pole motor.

It's important to stay within the safe design speed of whatever you are driving.

It's always best to look for the manufacturers specifications on your specific motor to see what they recommend.

In general though, all the standard industrial motors that "we" are likely to come across are designed to run at 3600 RPM, the speed of a 2-pole motor on 60 Hz mains.

Having designed them to do that, the manufacturer can safely fit a 4-pole (1800 RPM at 60 Hz) or 6-pole (1200 RPM at 60 Hz) winding, along with the rating plate to show that speed.
 
Tim (as usual) gave an excellent answer to the doubling speed ability of Chinese VFD.

Scott, I'd think the "normal" speed of a motor would be the speed listed on name tag for the motor.

Tim and I have went round 'n round on 1725 vs 3450 rpm motors. I could make a case for either. BUT - considering the use the motor is for, I still "think" I prefer the 3450 rpm motor for the cost saving aspect (edit: 3450 rpm motor usually less expensive). While the 1725 rpm motor will have a bit more torque at 900 rpm, the type of grinding at that lower speed requires so little power, I doubt even 1/2 hp is used.

I "think" my recommendation (suggestion) would be which ever is less expensive.

Ken H>
 
Last edited:
You must log in or register to reply here.
Back
Top