Grinder design questions: tracking wheel & drive wheel position, over-center tension, etc.

Good comments folks - Sorry I've been out of touch, wife had foot surgery yesterday and I've been sorta out of pocket for responding. I've been reading the posts, but I don't do much for typing on tablet or phone, I NEED a real keyboard for typing - just old fashioned I guess {g}

Fitzhugh, that's a really good drawing you did in Fusion 360. Here are a couple of photos of my tracking system. The first photo shows the tracking from front view. The 1/2"X2" wide bar (plate) laying on top is bolted to the tension arm with only one bolt allowing it to pivot in respect to the tension arm. The tracking wheel tab is bolted to the top plate and changes angle as the system is pivoted with the adjustment screw at front. The plate is bolted to the outside vertical bar which is also a 1/2"X2" aluminum bar with two bolts to hold it solid. The spring at rear that holds pressure on the system is shown at rear.
Grinder-Tracking-Front.jpg

The rear spring shows a bit better in the next photo. The system looks a bit rough, but it works good.
Grinder-Tracking-Rear.jpg

The proper setup is with the tracking wheel axle set exactly perpendicular to the tension arm in all positions. Tracking adjustment is made as the tracking wheel is angled a tad forward or rearward from perpendicular.

I like the idea of a ratcheting tension system but have not came up with design to build one yet that wasn't too complex. AND the spring system I've got seems to be working pretty good. I used a "prop" in place of the spring to test out the ratcheting system and while it worked good, it didn't seem to buy me much. Maybe I need to revisit? I do have to put a pretty heavy spring in place when grinding high speed with ceramic belts because they will "drift" to one side with grinding pressure without heavy belt tension.

Later
 
Ken, I hope your wife recovers quickly from the surgery.

Thank you for posting the pictures. Do you happen to know the specs for the spring you used, or can you guesstimate how much force is required?

I have not found a good solution for a DIY ratchet system either. Part of the problem is that I have no clue how much motion at the tracking wheel per ratchet click I should aim for. With my fabrication tools and skill, the gear teeth would end up fairly coarse, no smaller than 1/4" at best. My hunch is that the motion increment at the tracking wheel should be smaller than that, so some reduction would be required. The most promising idea I have come up with is to have an independent tension arm with a pivot point a few inches above the pivot point of the tracking arm. The two arms would be connected by a tension spring to adjust the amount of force per ratchet click. I plan to make a mock-up of this arrangement out of 1/4" plywood and rubber bands one of these days. I drew a sketch of it a while ago and it looked like it might work.
 
Wife is doing good - it was for a hammer toe (I'd never heard of that before) where they have to cut the big toe bone to get it straight, put screws in to hold bone in place. Then cut bone in 2nd toe to get it straight and put a screw in. Amazing how involved simple "toe surgery" can be. I watched a couple of youtube videos on the surgery before hand. Interesting how detailed those videos where.

On the spring - I have not idea how strong, it was an old spring I'd had for years and I'm pretty sure I got it at a hardware store with no specs available. It does need to be pretty strong, but no drastically so.

What about a fine tooth saw blade for the ratchet catches? I saw a 180 tooth saw blade 10" in diameter might be ok to cut a section from.
 
Ken H> said:
Wife is doing good - it was for a hammer toe (I'd never heard of that before) where they have to cut the big toe bone to get it straight, put screws in to hold bone in place. Then cut bone in 2nd toe to get it straight and put a screw in. Amazing how involved simple "toe surgery" can be. I watched a couple of youtube videos on the surgery before hand. Interesting how detailed those videos where.

On the spring - I have not idea how strong, it was an old spring I'd had for years and I'm pretty sure I got it at a hardware store with no specs available. It does need to be pretty strong, but no drastically so.

What about a fine tooth saw blade for the ratchet catches? I saw a 180 tooth saw blade 10" in diameter might be ok to cut a section from.
Click to expand...
Glad to hear your wife is doing all right.

If the spring has to be pretty strong, the two plates will have to be a bit further apart than what I had in mind. Looking at the stock springs at McMaster, I can find something that would give about 10 lbf with around a 1" gap and have about 3/8" of travel.

I just looked on the internet and found a couple of 180 tooth blades, but they are pretty thin. They might work, but for some reason, the thought of putting a blade with sharp teeth on a grinder does not appeal to me. Most likely, I will go with a gas spring on my first grinder build. I really want to start building something. My plan is to build a frame similar to bjansen's and add a tilt stand so it can go horizontal. With the amount of shop time I get, that will take a couple of months or more...
 
Here is a McMaster spring that's darn close to what I'm using. This one is 3" long, I cut to length desired. While looking for a spring I found some shorter springs but they were more expensive. This one is $2.67 each
https://www.mcmaster.com/9657k22
The dimensions of my spring is wire diameter = .125"; OD of spring = 1.218", ID of spring = .974". I would use these dimensions as a guide only. The space between the two bars is around 3/4", so anywhere in that range is good. I planned for the outside bar to be parallel with the tension bar with the tracking wheel parallel, but it didn't wind up that way, but close.

Good luck, you're gonna have fun building the grinder. I enjoy building tools almost as much as making knives.
 
Hubert S. said:
Glad to hear your wife is doing all right.

If the spring has to be pretty strong, the two plates will have to be a bit further apart than what I had in mind. Looking at the stock springs at McMaster, I can find something that would give about 10 lbf with around a 1" gap and have about 3/8" of travel.

I just looked on the internet and found a couple of 180 tooth blades, but they are pretty thin. They might work, but for some reason, the thought of putting a blade with sharp teeth on a grinder does not appeal to me. Most likely, I will go with a gas spring on my first grinder build. I really want to start building something. My plan is to build a frame similar to bjansen's and add a tilt stand so it can go horizontal. With the amount of shop time I get, that will take a couple of months or more...
Click to expand...
Here is my ratchet mechanism , it can t be simple than that.Maybe you will like it :)
https://bladeforums.com/threads/ratchet-mechanism-on-belt-grinder.1554914/
 
Natlek - using a parking break ratchet was clever. As someone commented on that thread it does look like the teeth are reversed, but only because I was expecting the catch to hang from the tooth instead of pushing into the tooth as yours does. With it that way it could probably even be aluminum, though you proved toothy things are abundant if one looks.
A 4" hss circular saw blade could be a cheap source. 10" is pretty large to try and fit.
Do you have a shot of the complete grinder?

Ken, hope you're spoiling her - toes may be small and generally ignored but when they're not working?

I see I forgot the spring entirely in that scteenshot. I can't tell in the photos that the bars don't line up. all that matters of the belt tracks.

Regarding the screenshots, I pretty much have to add a surface appearance to each part or the whole thing looks like one continuous mass. you can't see where one part ends and another starts. The "brushed aluminum" appearance just happens to work well since you can orient the lines, only takes a few clicks. The alternative is letting it assign random pastel colors to everything, looks distractingly like it's intended for use in a baby's room.

Hubert - I'll have cash to order the material in a couple weeks. The cable glands arrived yesterday so I'll get the wiring and hook up the VFD and motor this weekend.
 
Ken H> said:
Here is a McMaster spring that's darn close to what I'm using. This one is 3" long, I cut to length desired. While looking for a spring I found some shorter springs but they were more expensive. This one is $2.67 each
https://www.mcmaster.com/9657k22
The dimensions of my spring is wire diameter = .125"; OD of spring = 1.218", ID of spring = .974". I would use these dimensions as a guide only. The space between the two bars is around 3/4", so anywhere in that range is good. I planned for the outside bar to be parallel with the tension bar with the tracking wheel parallel, but it didn't wind up that way, but close.

Good luck, you're gonna have fun building the grinder. I enjoy building tools almost as much as making knives.
Click to expand...
Thanks for the details on the spring. I really like building tools and look forward to getting started on the grinder.
 
Not sure if you'll find it worth the hassle, but I found I could save a fair amount by ordering aluminum from 2 places, xometry.com and midweststeelsupply.com. The pricing for different sizes is odd. Xometry ships free, but a few things were cheaper with shipping from MWSS.
Likewise, I'll order a few parts like the gas shock from McMaster Carr but all the nuts and bolts I'll order online and pick up at the local fastenal.
I'd share the breakdown but it's not helpful since it doesn't match the original plans.
Let us know what you do regarding tracking, and thanks for all the helpful input.
 
Fitzhugh said:
Natlek - using a parking break ratchet was clever. As someone commented on that thread it does look like the teeth are reversed, but only because I was expecting the catch to hang from the tooth instead of pushing into the tooth as yours does. With it that way it could probably even be aluminum, though you proved toothy things are abundant if one looks.
A 4" hss circular saw blade could be a cheap source. 10" is pretty large to try and fit.
Do you have a shot of the complete grinder?
Click to expand...
Here....................https://bladeforums.com/threads/my-new-2x42-toy.1571543/
 
Fitzhugh, I think you will be done with your grinder long before I get to my tracking arm... I will post progress updates when I start building.
 
OK, ya'll just cost me some money this morning. I looked at midweststeelsupply.com and they do have good prices on aluminum, and decent shipping. Just wish I lived close enough to pick it up... No, wait - they're up in Mn, I do NOT wish I lived close to them, wish they were close enough to me here on the coast! It's too cold up there.

I didn't see any metal for sale on xometry.com, more of a machining site.
 
Ken, xometry has aluminum under the Supplies category. They have good prices and free shipping over $50 dollars (as long as the items meet weight/size requirements). But don't go looking, it might cost you some more money.
 
xometry does have very decent prices, while it's a small tad more than midweststeelsupply.com per piece, it more than makes up for it in shipping. Especially if you're only needing a small amount. I just compared prices and if I'd found the aluminum on Xometry before placing the order I'd saved perhaps $20 or so due to shipping. I WILL remember Xometry.com
 
Ken, did you order the aluminum for another grinder build?

One annoying thing about xometry is sometimes the free shipping option disappears for no apparent reason. It has to do with either size or weight, and you have to either break up your order or change lengths. I ordered two 6' long bars from them a few weeks ago and they shipped free, but now they want over $100 for shipping the exact same order. If you break it down into shorter bars, they still ship free, but it is a bit more expensive and you likely end up with more scrap unless you plan out exactly what you need ahead of time.

I just watched a video by Marius Hornberger about cam levers for MFT style tables. I wonder if you could use a cam lever instead of a ratchet for the tension mechanism on a grinder. Like on the movable jaw of a Klemmsia clamp, only you would push up the tracking arm instead of the clamp pad. Or put the cam pivot on the tracking arm and let the cam push against the top of the grinder frame. This seems almost too easy, there must be a catch. Maybe not enough friction or not enough travel. Has anybody tried this?
 
Naw, not really planning to build another grinder just yet. The one I've got works good and don't do enough knifemaking to really need another grinder. I do have an idea I might rework the horizontal grinder and use it for the SGA attachment. I got a spindle sander a couple weeks ago and it seems like it's going to replace the small wheel attachment I used on the horizontal grinder. While I still use the horizontal grinder, not as much as before. The way I'm planning I can still switch between SGA and horizontal setup. We'll see how that works out.

On the aluminum ordered, I'm always finding one project or other where I use aluminum,.
 
Natlek, that's a very nicely built, compact tension and tracking mechanism on a resourcefully made grinder. Are longer belts hard to get where you are?

Good to know about the odd shipping from xometry. Looks like 58 inches ships free, at least right now(??), but 60 inch long costs $101 to ship. Ouch. No doubt a weight limit as well as Hubert said.

Anyone have advice on cutting up the aluminum stock?
My plan is to cut 1/2 x 1.5 and 1.5 x 1.5 bars to length on a miter saw with wax as a cutting lube. Bad idea? Options? Do I need a non-ferrous cutting blade, or can I use a cheap general purpose 60 tooth 10" carbide blade I don't care about?

I can order it all cut to length for about $10 more from xometry (or $25 more from MWSS) but I have no idea how accurately they cut it.

Hubert, you might need a large cam. I think the latter just uses linkages to get the same result.
 
Fitzhugh said:
Anyone have advice on cutting up the aluminum stock?
My plan is to cut 1/2 x 1.5 and 1.5 x 1.5 bars to length on a miter saw with wax as a cutting lube. Bad idea? Options? Do I need a non-ferrous cutting blade, or can I use a cheap general purpose 60 tooth 10" carbide blade I don't care about?

I can order it all cut to length for about $10 more from xometry (or $25 more from MWSS) but I have no idea how accurately they cut it.
Click to expand...
I have cut a lot of aluminum with a regular saw blade. I never use any lubricant. Just go slow. Wear ear and eye protection and don't trap small pieces between the blade and a stop block.
Fitzhugh said:
Hubert, you might need a large cam. I think the latter just uses linkages to get the same result.
Click to expand...
Not sure what "the latter" refers to.

I think a cam with a base circle of 1.5-2" and a displacement of 1/2" or 5/8" should work. This would get multiplied by a factor of 3 at the wheel with the geometry I have in mind. I looked up the static friction coefficient for steel and it is around 0.6 dry and down to 0.15 or so lubricated with grease. I think I will write a small program to calculate what friction will be necessary to lock the cam, or to find a geometry that works. I could not find anything online that would allow one to do that, but I think it is not overly complicated. If this works, it would be easy to fabricate in the home shop and give you continuously variable tension. But most of my brilliant ideas only work flawlessly in my mind...
 
Great news about cutting aluminum, thanks! The only thing I found online about cutting bar stock of any thickness was a video that did not seem that convincing. I'd rather cut everything but the larger side and base plates even if it's less than $10 more to have it cut. That way I can order extra and adapt as I go. I'm sure I'll find problems in the design as I work. The only part that isn't trivial cuts is the platten trunnion. I'll try it on a router jig, but if I flail I'll borrow time on a cnc router - it's just a bit of a drive.

"the latter" refers to, um, well I guess I deleted some text and didn't realize it. I think I was attempting to say that the linkage setup of the "cam-over" or "over center" style, as used by Drew Riley (https://www.bladeforums.com/threads/decided-to-build-my-own-grinder-almost-done.1382431/), kadrmas grinders and so on, works basically like a cam, but I realize I missed your whole point of having it actually variable vs. just toggling on or off. Your idea seems to work in my brain as well - but I wouldn't exactly see that as reassuring :)
If friction does't pan out I think you could just add a clamping nut/handle on the cam's axle that locks it into place.

This makes me realize I'm confused by one aspect of the ratchet style... With no spring involved, you tension it by pressing against the slight flex of the belt itself, right? Seems similar to a system with a very short throw, very strong spring... Lots of tension as long as you have the spring compressed but you lose all of it with just a little movement. So, with a ratchet, what happens when the belt stretches a bit in use? Won't you lose all tension?
In this case other peoples' brilliant ideas only fail to work flawlessly in my mind, since apparently they work brilliantly in reality.
 
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