Thread: Grinder pulleys

I have just about got my Hercus 3 grinder up and running. I was planning a modification that I will post once I have this first issue sorted. I checked the pulley sizes and with the motor running at the advertised 1440 rpm I would have a spindle speed of 4300 rpm. This is above the Hercus stated 3500 rpm and is pushing the limits for some of the grinding wheels.

The present setup is 2 V belts and the belts are not running smooth due to age.

The belts are old and were going to be replaced but it looks like I will also need at least one new pulley.

On other tool grinders I have seen either flat or toothed belts.

I was leaning towards a flat belt but cannot find suitable pulleys. I must be using the wrong search words. Should I keep going down the flat belt path or will a toothed belt give as smooth running. I may as well get this right and go with the best solution. If flat belt I may end up making pulleys out of aluminum.

Thanks Steve

Hi Steve,

If you're going to make own pulleys in order to get the speed right, then flat belts have the advantage that they are very common and easy to get or make. A good source of flat belts are those used on vacuum cleaners and the like. They re also relatively cheap.

Otherwise I would look at commercial toothed belt pulleys and buy the correct sizes to suit your need. The downside to these is that you might have to make a tensioning device.

Hi Steve, I used a 5 row Multi V belt, about 15mm wide, or sometimes called a Serpentine belt, a similar belt would be probably on your car, driving the alternator, air conditioner etc., on my surface grinder.
I did have to get some special pulleys made, thanks Michael.
HTH
Kryn

Originally Posted by Reidy41

Should I keep going down the flat belt path or will a toothed belt give as smooth running.

Maybe...
I would be concerned that a toothed belt would be slightly 'jumpy' because of the teeth. Probably barely noticeable, but while non-toothed versions can slip slightly, they are smoother in their power delivery. My vote would be for flat or V (either traditional or poly-V)

Michael

Thanks for all of the replies. The project that lead me to checking the speed of the work head come from me thinking about sharpening Carbide scrapers.

I was lying in bed last night and it occurred to me that I all ready have a device in the shed that is designed to spin disks at a certain speed.
For those of you not familiar with the Hercus T&C grinder, they have a mount on the side of the workhead for attaching a high speed internal grinder.
A large pulley is mounted where the grinding wheel normally goes and there is a small pulley on the internal grinder which is set up for around a one to ten ratio.
The mount is not much more than a clamp that will take a 20mm object and the grinder is not much more than a hollow bar with a big bearing at the front and a small one at the back.

The light bulb come on, if I mount a small pulley on the work head and the large pulley on the thing I am going to make that looks similar to the internal grinding attachment,
I will end up with a speed of around 350 rpm. Almost perfect speed for a lap. I am planning a 3 phase motor and VFD down the track so anywhere between 200 and 400 should be achievable. I will just have to make a small mount that bolts two the T slot and I have a carbide lapper, slow speed grinder. When not in use it will take up very little storage space.

Steve

Does anyone know if there is a set curve for design of pulleys for the use with Daclon flat belts, or can I just make them flat and put a fence on one pulley?

Thanks Steve

I think there are specific calculations for dimensions of the crown section of a flat belt pulley in the Machinery’s handbook.

Elasticity of the belt and width of the pulley is probably a factor in calculating the radius of the crown.

If the width of the pulley is similar to the Waldown TPG grinder then probably it’s easier to copy it from because they use Daclon flat belts.

I think the internet is making my lazy/dumber. In my younger days I would always go to the bookshelf and grab a reference book. Now I will at times forget I may have the answer. I had a read of my copy of the Machinist handbook, which I got from a very generous forum member (Micheal G) and it just gives guidance. More curved for leather and low speed. From the way I read it if I put a small dome it should work. My plan is a small dome on the motor pulley and a fence on the small pulley. I should end up with a belt and braces solution.

Steve

Found this on Google; https://www.tec-science.com/mechanic...belt-on-track/

https://www.slideshare.net/MohamedMo...oogle_vignette

https://www.google.com/search?q=crow...t=gws-wiz-serp

HTH
Kryn

Originally Posted by Reidy41

... From the way I read it if I put a small dome it should work.

From memory the rough rule of thumb I picked up somewhere was 1/8" crown per 12" width. It does not have to be much - I think I usually just use a file to shape the surface. The belts ride on the highest section, so a pulley with sides on it may not work well if the other shaft is not well aligned.

Michael

Thanks Michael

I have just come in from making the crowned motor pulley. I just decided to go with some crown would be good but I don't want to much approach. As it turns out the crown I ended up with is very close to the 1/8" per foot. I would have to to the accurate math but it would be around 3/32" per foot.

When I get the belt I will see how it tracks. I have fitted it to the motor and am getting around 1/2 a thou or less run out so I am going to call it done.
I will make the small one tomorrow.

Steve

Hi Guys,

I may have got this wrong but I seem to recall that only one of the two pulleys had a crown. From line shafts, only the machine pulley had a crown, the line shaft pulley was flat.

I had heard the one flat pulley thing but the Clarkson grinders had both domed. I understand some tool post grinders also have 2 domed pulleys. From that I can only assume that as long as one is domed it should work but does not matter if both are.

Steve

Hi Steve,

It been a lot of years since I did any line shaft work ! As much as I remember, the lower machine pulley was crowned so that when the belt was moved between the live and dead pulleys the belt stayed square on the machine pulley.

But I do understand that if both pulleys are crowned then the belt should stay stay square in the middle.