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

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Feb 5, 2013
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I'm slowly planning a grinder build based on B bjansen 's plans and build-along (thank you!), but bastardized heavily to use a base mount motor I already have and use just a few sizes of aluminum stock, since that cuts the cost a fair amount. These changes forced other changes, and so on. There are a few things I'd like help with.

First, does anyone have dimensions for a good over-center tension setup? I'd like to use one, but I'm not sure I should try unless I'm working from a proven design - I suspect a traditional setup would be easier to troubleshoot for a novice.

Second question: Can the drive wheel be mounted out a bit on the motor shaft, say by about 3/4"?
The set screw would still fully engage and no bearings are involved.
1M0WjA9.png


Last question: How much does the belt have to wrap around the tracking wheel for tracking to work well?
I'm trying to mount the motor a bit behind the chassis for a few reasons: so the junction box does not crowd the tool bar clamping handles, to keep the length of tool arms down.

Does this look OK?
32svFg4.png


Here is the original, which is more in line with other grinders I see online:
tLSYRgb.png


If it does matter I could move the motor up so the belt path looks more like grinders I see out there, but either the junction box crowds the tool arm clamp handles, or I have to drill and tap some really awkward holes on the motor housing for the fan shroud so I can flip the rotor and put the junction box in the rear:

ybVnkNl.png



Design so far:
lkf5zjp.png

I'd appreciate any feedback, especially anything that looks poorly thought out. I don't actually know what I'm doing, haven't built or even used a full size grinder but it's a fun project. In other words... Don't build this, it probably sucks in many ways I can't imagine. DO build the well proven bjansen design.

Right now it's coming in about $300 in material and hardware, or $630 with budget options for wheels, vfd, motor. Using better wheels, KBDA-27D and free motor, nice wiring it would cost about $850.

The VFD arrived a few days ago. I had planned on using a cheap import before realizing that wasn't as easy without 220 so I'll have to save a bit for the rest of the materials, but no going back now :)

[edited to clarify I meant "don't build this mess, I don't know what I'm doing. Build the real version"]
 
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Looks good. You could solve the junction box clearance issue by putting the motor on the right side. I have seen a few grinders using treadmill motors set up like this, I think because the motor cannot be reversed.

I have been looking at building a grinder myself and have not seen any designs for over center cam tension systems with dimensions. IIRC, Drew Riley (member here, arcustomknives I think) built one, but I do not think it would fit onto your grinder. He has some youtube videos explaining his tension mechanism.
 
What program are you using to draw up those designs? You've done really good, that final design is professional looking CAD work. With that said, how far back the motor is determines the length of belt. You want to keep belt length to 72" if you're wanting a 2X72 grinder. You should be able to use the drafting program to check properties of the belt to get full lenght.

Yes, the drive wheel can be mounted out a tad on the motor shaft, as long as the setscrews engage good on the shaft.

The center of tracking wheel (tension wheel) location should be centered in the belt. ALL wheels really "need" to be lined up so the center of all wheels are in the same line. this is VERY important for good tracking.
dimensions for a good over-center tension setup?
I'm not sure what you mean by this question - The tracking (tension) wheel needs to be fairly close to same height as the top wheel on the platen wheel. What type of tracking adjustment are you using?

Since you're mounting the motor to a baseplate rather than using the 56C face mount be darn sure that motor shaft is square to the belt, and the motor shaft is parallel to the tracking and other wheels.

Good luck with the build, and any questions, this bunch is pretty good at helping.
 
I would recommend extending the side plate to incorporate a face mount of the motor.

This will give you two good benefits:
  • Better alignment between motor and chassis which will minimize your tracking problems.
  • The option to mount the motor upside down with the junction box to the back.
 
I would recommend extending the side plate to incorporate a face mount of the motor.
I know this is good advice, but I'm going to try it with the base mount motor for now and probably return and say "yup, you told me so". I can swap out the right side plate and convert it to a base mount later, if need be. (It's a matter of money - an iron horse motor wouldn't cost much, but I'm barely scraping this together already). I'll make sure it's very squared up and in plane with the other wheels.


Looks good. You could solve the junction box clearance issue by putting the motor on the right side.

I'll look for Drew's stuff, thanks.
Good point about motor mounting options - and it makes me realize this is not something I need to fully figure out ahead of time since I can try the motor in other positions.

What program are you using to draw up those designs?
Fusion 360 - makes spiffy renders with a click.
It's worth checking out: hobby use is free & fully functional. You'll find lots of support via its forums, youtube videos, etc. Plus, I think a number of members here use it. I use it for non-CNC projects a lot more than I would have thought.

If you are new to CAD try following along with a couple intro videos. I was hopeless when I tried my usual stubborn click and poke "I'll figure it out" exploring, but it became pretty intuitive and fast once I had a decent roadmap from watching some videos.

I'm happy to share the design if anyone is curious, but really, go with a proven design.

My question about wheel placement was poorly phrased. I have the wheels in the same plane, I'm just wondering if the belt wraps around the tracking wheel enough with the motor farther back. I can always play around with it if it is an issue.

Tension mechanism... apparently it's "cam-over" not "over-center." It looks like a nice addition, but probably not worth adding another thing to trouble shoot on my first grinder. I've drawn it up with the traditional tracking and tension setup, and have the belt horizontal between tracking and top idler, as you mention.

Good luck with the build, and any questions, this bunch is pretty good at helping.
Thanks. You're partially to blame for me falling down this rabbit hole :) I looked into it a few years ago but gave up because I don't weld and didn't have the funds. Recently I saw your posts saying aluminum grinders were pretty easy to build , found VFD prices had dropped a bunch, and I got a free motor. Luckily by the time I realized I had fewer budget VFD options (no 220) I was stuck on the idea. I've got a KB under my desk, just means it will take another month or two to buy the rest of the stuff.
 
Fitz, what you are proposing will work fine. I have built one like that as well and still use it to this day - the geometry of the belt to the tracking wheel is very much like you posted.
 
Good point about motor mounting options - and it makes me realize this is not something I need to fully figure out ahead of time since I can try the motor in other positions.
Just to be clear, what I meant was putting the motor on the right and the wheels on the left of the frame. I think this might require a little bit of pre-planning...
 
Fitz, what you are proposing will work fine. I have built one like that as well and still use it to this day - the geometry of the belt to the tracking wheel is very much like you posted.
Great! Thanks again for sharing your plans and answering all my earlier questions in email.
Oh, one question I was going to ask in your plans thread... can I get away with leaving out the thrust bearings in the tension pivot joint? Aluminum sliding on aluminum [tracking arm on risers] seems fine since there is no load and it's only when adjusting... but will grit and swarf getting in there be an issue?

[Side note: seriously Google? I'll have a lot more faith in AI when my phone is smart enough to know I'm really not trying to ask if dwarves will be a problem. Get that right, and then we can talk about letting you drive. But don't get your hopes up.]

Without them the three 1/2" thick pieces bolt nicely onto the top tool arm spacer with flathead screws from the bottom. I went with a bar stock center piece instead of the 4 round spacers between the risers, with the center piece extending forward to give it a bigger footprint since it's threads under tension instead of screws under shearing load. (I'm probably over thinking it)
 
Just to be clear, what I meant was putting the motor on the right and the wheels on the left of the frame. I think this might require a little bit of pre-planning...
Yeah, I understood that. I had not considered it until you mentioned it. I think I'll plan on trying out different motor positions and then remounting the whole setup on a fresh base if need be, or more likely just live with lots of holes.
 
I have the wheels in the same plane, I'm just wondering if the belt wraps around the tracking wheel enough with the motor farther back
I didn't pick up on that - your question is if the less "wrap around" of the belt on tracking wheel will affect tracking. I do think you'll have plenty of tracking control - doesn't take much belt on the tracking wheel to provide that. Since you're using a foot mounted motor you could also use motor adjustment for tracking like the TW-90 does.

I "think" motor tracking might be one of the best methods, I've not tried it yet. I did change from the old KMG type tracking that's used on most grinders to the new Reeder Grinder method of tracking control. It's pretty easy to make, here's a video showing it:

Fusion 360 is a good program, I never liked having to be connected to internet to use it, and didn't they cancel the freebie version? Draftsight did that with their free version. Draftsight was my favorite since they had a Linux version and was an AutoCAD clone. I've used AutoCAD professionally since version 2.62 way back in DOS days.

I'm now starting to use NanoCAD - it's a freebie, but doesn't have a Linux version.

THANK YOU bjansen for a very good design that's well suited to home building.
 
Great! Thanks again for sharing your plans and answering all my earlier questions in email.
Oh, one question I was going to ask in your plans thread... can I get away with leaving out the thrust bearings in the tension pivot joint? Aluminum sliding on aluminum [tracking arm on risers] seems fine since there is no load and it's only when adjusting... but will grit and swarf getting in there be an issue?

[Side note: seriously Google? I'll have a lot more faith in AI when my phone is smart enough to know I'm really not trying to ask if dwarves will be a problem. Get that right, and then we can talk about letting you drive. But don't get your hopes up.]

Without them the three 1/2" thick pieces bolt nicely onto the top tool arm spacer with flathead screws from the bottom. I went with a bar stock center piece instead of the 4 round spacers between the risers, with the center piece extending forward to give it a bigger footprint since it's threads under tension instead of screws under shearing load. (I'm probably over thinking it)
I have not built a grinder, just looked at bjansen's plans, so take this for what it's worth... I would want a washer/thrust bearing in there to control where the friction occurs and to be able to take out play. If everything is nominally parallel with no clearance, it might bind somewhere far from the pivot point, which would be more difficult to deal with.

If I understand your plan correctly, you want to bolt a spacer and the left and right tracking supports to the top tool arm spacer from underneath instead of bolting it to the main plate. One nice feature of bjansen's (and many other's) design is that the plate aligns the motor, the tracking arm and the tool arms. With your design, you would lose that for the tracking arm and the motor. The motor is relatively easy to adjust, but the tracking arm would be hard to get to, since the bolts would be inside the top tool arm slot. The pitch and roll axes don't matter, since the tracking arm pivots around one and the tracking knob adjusts the other, but the yaw might be an issue. I don't know how big a problem this is, but from researching grinders it appears to be a recurring theme. The Reeder grinder has a dual axis tracking mechanism to compensate for it. I believe Drew Riley also added an adjustment for it on his DIY grinder, maybe he'll chime in. I vaguely recall reading about this issue in Dan Comeau's Sayber OSG grinder manual as well (I think he adjusts for it by tapering a spacer used to attach the tracking hinge). More recently, I watched a youtube video by a guy named House (IIRC) who built a welded grinder and made his tracking hinge adjustable for yaw (not a design I would copy as it only locks with the pivot bolt). As you can probably tell, I have been looking at grinder designs too much... I guess what I am trying to say is that it might be a bit more difficult to get the tracking right if you don't get the tracking support perfectly aligned by bolting it to the tool arm spacer instead of the main plate. Probably not a big issue as long as you get it close enough.
 
I made my own grinder too... If I were to do it again, I'd make a frame that the motor bolts to directly. I still have to screw around with the motor and wheels to get it to track right...

Also, I'd put in a ratcheting tension system rather than a spring or shock.
 
A.McPherson - I tried coming up with a ratchet I could make, but am limited to woodworking shop tools. You never found a sweet spot for the motor to just stay bolted in place? I was hoping it was just a matter of initial tweaking and tuning.

Hubert - I've been doing the same, looking at all the designs until my head spins. It's taking me longer to get to building than I had hoped - life and money - but it means I can work out the details more.
That's a really good point about the tracking bolting to the side plate. I understood about losing that with the motor mounted to the table, but had overlooked the obvious implications of moving the tracking. I'll look at adding the yaw like Ken linked to in the Reeder grinder, and/or adding some reference surface connections between the side plates and the tension risers.

Ken - do you have a photo of your new tracking setup? I get how they work, just curious to see various approaches of how to put one together (I'm trying to stick with bolting rectangles together and avoid having to cut out a section of a bar, like where the tracking tab attaches to the pivoting piece on top. I could do it on the table saw, I guess.)
I tried every free linux option I could find about 5 years ago before breaking down and installing windows dual boot, so I know that pain well. I never did get draftsight to run without crashing, and all the other options where odd ducks in one way or another. The fact I had no idea what was normal or expected in CAD programs did not help.

I've only really used sketchup and F360, and hated sketchup and F360 exported gcode - can't say if it's worth looking at since you have tools you know, and probably expect a lot more from your CAD programs than I do, but there is a free version still. They changed licensing recently, but mostly by splitting it into free for personal use (lacks some teamwork features), and free for startups making under 100k/year and/or under 3 years old (I think[/] it's "or"). You can work offline, but with limitations. There's something about offline cache duration limited to two weeks, I think, and of course you can't raid the McMaster Carr catalog for models of threaded inserts, gas springs, etc. :( If you do look at it be sure and try generating drawings of some parts. Making drawings is easy, making nice drawings not so much since you just don't have much fine control. I'm surprised since they did a good job on the rest, from what I can tell.

Thanks all!
 
Fitz, it was answered already but I would use those thrust bearings not as much for the friction reduction but more so for the clearance they provide between the tracking tab and the two pieces that hold the tab. I am not certain how the KMG is set up (maybe no thrust bearings) but I think some clearance will help especially if you are drilling/tapping by hand which may get you a thousand or two off from perfectly parallel.
 
Hey Fitz, yeah I never have gotten it to the point that I can switch back and forth between platens, wheels, etc. without having to really mess around with things.

I think it has more to do with my crap skills than anything else. Well that and my crap design. I used a welded tube design, not one based on plates.

That being said I think a design for making a ratcheting style tensioning device shouldn't be that hard...

I'm on my phone at a hotel, but I'll see if I can find a doodle app or something and draw something up really quick.
 
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Maybe something like this?

Jys4zTy.png

Basically a plate of metal with notches that a piece of steel rod locks into. It might take a little messing with to get it working correctly, but I think it's do-able with wood working tools.
 
It's pretty easy to make, here's a video showing it:
For some reason, I cannot understand what he is saying on the video. Even at full volume, I can barely hear him.

It appears that the roll and yaw adjustments are not independent. It looks like the adjustment knob for the roll angle is fixed to the tracking arm and does not pivot with the yaw adjustment, i.e., when you adjust the yaw, the roll is changing as well. Maybe I am misunderstanding something. It looks easy to build and I think I might do something similar when I build my grinder.
 
Good point bjansen - I'm probably being way too optimistic about my drilling and tapping results. I'll practice and get sense just how accurate I can get on my setup at home.

A.McPherson - don't sell yourself short, you made a grinder :) I can't imagine it is all that possible to get one that runs consistently true when starting with square tubes that aren't all that square.
I went and looked at ratcheting tension setups and I see the appeal, but for this first build I want to keep it simple. So far the only parts that aren't just cut square, drilled or tapped are the D-Plate (router table will do) and the platten mounts (chain drilling and filing, or I'll just buy them). I did see a thread that shows a few WIP grinders, one using a car handbrake ratchet, a cut up saw blade, etc.

I also came across a video from JTKnives where he replaced the spring with a car jack.... basically terrify the belt into behaving:
 
Hubert, I overlooked your reply.
That's odd, the video does have decent audio when I play it. There is a fair amount of noise in the latter part but the voice is clear then as well.
I did a quick mock up something like the Reeder tracking setup after seeing your comment... looks like changing the yaw won't actually impact the standard/roll tracking angle much at all. If it is an issue grinding a semi-spherical arc on the end of the roll tracking knob threads could essentially get about 10 degrees each way without any impact. I figured it would need a wide mushroom head thingy on the end of the traditional tracking knob threads, but it would work with just a small arc ground on the end (if it's needed).

[I'm just nerding out on this because I can't start building my grinder yet].

From rear, wheel axle bolt on left:
TFKNzM8.png


Top, no adjustment:
rOCMgok.png


Top, large [9 degrees] adjustment in yaw tracking:
ZXDG2aI.png
 
Hubert, I overlooked your reply.
That's odd, the video does have decent audio when I play it. There is a fair amount of noise in the latter part but the voice is clear then as well.
I did a quick mock up something like the Reeder tracking setup after seeing your comment... looks like changing the yaw won't actually impact the standard/roll tracking angle much at all. If it is an issue grinding a semi-spherical arc on the end of the roll tracking knob threads could essentially get about 10 degrees each way without any impact. I figured it would need a wide mushroom head thingy on the end of the traditional tracking knob threads, but it would work with just a small arc ground on the end (if it's needed).

[I'm just nerding out on this because I can't start building my grinder yet].

From rear, wheel axle bolt on left:
TFKNzM8.png


Top, no adjustment:
rOCMgok.png


Top, large [9 degrees] adjustment in yaw tracking:
ZXDG2aI.png
Fitzhugh, thank you for the drawings. I had thought that grinding an arc with a radius equal to the nominal distance from the pivot point would help it, but it seems to be a really tiny effect to begin with. This mechanism should be fairly easy to incorporate. I think a tension spring near the yaw control knob instead of the compression spring on the Reeder would make it more compact and fit better on a grinder with a shorter arm between the tracking wheel and the pivot point of the tracking arm.

When do you plan to start building?

I figured out the audio issue. I clicked a check box in the audio driver to send it through HDMI instead of "line out" and it played. The strange thing is that this is the first video on youtube that I have ever had this issue with. I checked out some of the other Reeder grinder videos and the older ones all have the same issue on my computer.
 
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