Thoughts on my belt grinder design

J

javajaws

Joined
Oct 22, 2015
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38
I've been putting this design together the last couple weeks and hope to start building soon. But before I start burning money, I thought I would run this past you guys since you'll have such a vast amount of experience with these things.

This will be a direct mount VFD driven grinder capable of vertical and horizontal grinding. Construction will be primarily 1/4" plate welded together. Other than supporting a direct mount motor and having multiple tooling slots, my main goal was to design something I thought I could actually build (I have metalworking and welding experience but no cnc equipment).

I didn't initially plan on having 5 tooling slots, but I wanted the midpoint of the platen to be at a certain height for comfortable grinding and the math just worked out that way. I could have left the space empty down there but then I would have had to add a brace anyway. So...why not? :)

Another mid-design idea I came up with was to put the gas spring on the wheel side of the frame. This gave me more room for the spring without having to increase the height of the tracking wheel...and allows me to run with the tension arm horizontal (not something I have seen much of when using a gas spring so far). I've checked clearance with multiple belt configurations and I'm pretty sure I've got enough clearance in all cases. I even have room to move the mounts around a bit (leaving that to a build time call). The gas spring isn't mounted exactly vertical so it will lose some of its force - but it is mounted further out than the wheel along the tension arm so that should help compensate for that. And I see advantages in mounting the gas spring on the same side of the tension bar as the tracking wheel: the twisting force caused by the gas spring should be offset by that incurred by the tracking wheel.

grinder_2_zpscaksnvk3.png


BTW, the slots you see on the side of the frame are for welding the side to the horizontal tool supports. This way you don't have to grind anything off from the other side where clearance is an issue. I'll probably add another row farther back - I just haven't put them in there yet.

grinder_3_zpsgj0fwsgg.png



Here's the backside showing the toolbar supports and braces that allow the whole thing to be flipped while still fully supported.

You can't see very well in this picture, but the mount for the tracking wheel is adjustable such that you can make sure it runs parallel to the frame (somebody's mod to the GIB I read around here...thx!). Handy in case something in the build process causes things to get out of alignment.

grinder_1_zpsxsml9d2m.png



Here it is flipped horizontal. The motor doesn't clear without a cutout, but that was partly by design: In order to clear the table the belt would have been higher in the horizontal position than I wanted (like ~14" or so above the table with room for air to get into the fan). So to keep the height of the belt down I had to keep the flip point closer to the frame...which isn't high enough when vertical for the motor to clear. I plan on making a dedicated stand for this, so it wasn't a big deal to me.

grinder_4_zpsgmu4rink.png



...and yeah, I've calculated the belt lengths! I'm within 1" for both the platen and 8" wheel models...close enough for me to know it'll fit with slight movement of the toolbar! :) And using the top tool support it should fit a 14" wheel without a problem.

Right now the length from the middle of the motor spindle to the front of the platen is about 24". Does this seem too "long" or about right? I could always raise the tension bar to shorten that if I need to.

If anyone sees any obvious gotchas or has any ideas I would love to hear them!
 
I have built and modified two belt grinders and have given design a whole lot of thought. I like your design a bunch but I have a couple points to make. First, If you make the base a little wider then you could put a hinge there and have the motor sit an inch off the table eliminating the hole. Second, I really do not believe that you need 5 slots for tool arms so I would redesign it for the top three openings for tool arms. This would simplify your build a lot. Third, consider using a shorter gas piston so that It can be mounted more vertically. 30 Ibs. is about the right pressure. Mcmaster Carr has several sizes. Last, I would use a 3 phase 2 hp 1725 rpm motor with an 8 inch drive wheel rather than a 3450 rpm motor with a 4 inch drive wheel. I think the drive wheel may be found from the Bader grinder parts. Also, You may be able to buy the platen frame from Polar Bear Forge cheaper than you can make one. My opinion from trial and error building. Oh, and you will need a 220 volt outlet for the motors that I recommend. Good luck! Larry
 
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Hey Larry, thanks for the feedback!

As for the motor and wheels...I actually had already bought them (I wanted them on hand before I started building for checking measurements, etc). I'll be running a 1725 1.5 hp motor with the 2x option on the VFD and a 5" drive wheel. I really needed this to run on 110 so I purposefully limited myself to 1.5 hp. Though if I want to upgrade in the future I could run 220 with the same VFD and a new motor.

I'll look into seeing if I can make the gas spring vertical - but what difference would that make? The tension arm doesn't know what angle the spring is - all it knows is what upwards force is put on it (assuming the pivot point is braced enough to offset the forward force generated by the angle). I admit some upwards force is lost by the angle, but this is offset by being further out on the arm than the wheel (so it will have roughly 1.3x the force on the wheel). The total force on the belt is really just a math calculation. I suppose the angle could make the rebound time slightly longer since the piston has farther to travel - is that an issue on these grinders? Do you find the piston compressing/decompressing a lot during use? Or is it pretty much at a constant length?

What would you have me do instead of the bottom two slots? There's only 3 pieces of metal there to make that happen which also helps the left side act as a brace. If I take those out I would have to add a brace - most likely perpendicular to the front toolslot openings (I actually have a version somewhere that did exactly that). I just found the 5 slots more aesthetically pleasing from a top/bottom symmetry perspective.

On flipping and hole in the table - like I mentioned I did that because I wanted the belt at a certain height (I get carpal tunnel so I have to pay attention to things like that unfortunately). At what height or arm position do you find most comfortable? I had planned on being able to keep my forearms parallel to the ground for the most part. But as I think about it maybe that is too low (neck/back strain).
 
I don't see any reason for all the tool holders as you have to remove 1 to use another.
 
Well, true enough. I have seen some setups where people put 2 small wheels on a belt at once though - but I'm not production grinding and I doubt I would do that anytime soon if ever.

The biggest benefit I see though is flexibility in placement (both when vertical and horizontal). Lets say I'm horizontal and I want to work off the right/bottom wheel of the platen (I'm a lefty so this is likely). It would be great to put the toolrest in the right/bottom most slot to work off that end.

Here's what it could look like with only 3 holders though. But to be honest, this doesn't really save me much time/money. Maybe $15 in metal and an hour of work.

grinder2b_zpsgp2eawhy.png
 
can i ask why you have all the small vertical pieces on the left side instead of a single plate? and why not extend them the length of the horizontal sections of pockets? the tool pockets will only be as strong as the weakest weld forming the box. you should consider a 4 1/2'' hole for the motor mount. the horizontal support bracket is a bit overkill and will just add weight that you have to flip imo,
 
I agree with mike-E, why all the vertical pieces? I think you can simplify the design a great deal by having both sides one piece and having them extend up to provide the vertical support for your idler/tracking arm. and I would extend the right side to provide a mount for your motor. Take a look at the Wilmont 3 arm TAG grinder and follow Chris's lead.
 
mike-E said:
can i ask why you have all the small vertical pieces on the left side instead of a single plate? and why not extend them the length of the horizontal sections of pockets? the tool pockets will only be as strong as the weakest weld forming the box. you should consider a 4 1/2'' hole for the motor mount. the horizontal support bracket is a bit overkill and will just add weight that you have to flip imo,
Click to expand...

Motor mount: There actually is a 4.5" hole there - but the drive wheel is 5" and you just can't see it from these images.

So one solid plate on the left vs multiple smaller plates: It really came down to ease of building - there's not really any other reason than that. Since I am welding the frame together if I were to do another solid plate on the left like on the right I would have to weld through pockets cut into the plate to weld it to the horizontal pieces (welding from inside isn't an option along the full length...and the weld would interfere with the toolrest clearance anyway). This would mean more drilling/cutting by hand vs cutting those smaller pieces with a bandsaw. By using the smaller plates I can edge weld them (with proper bevels ground before welding for strength). I can guarantee you it will be stronger this way than if you had used bolts or pocket welds. If you've seen that yellow grinder on ebay that's what I would have to do essentially...which isn't the easiest without a mill or cnc.

Horizontal support: I'll definitely see how stable it is without it before I put it on the real thing. It's not critical in the other parts of the build and isn't needed to keep things aligned so I should be good to make everything else without it and see.
 
just to add my two cents on the 5 pockets, you might find the bottom pocket useful.you could have a tool arm with some type of swiveling hook at the end that will hold a quench bucket that can be adjusted in and out. i would keep the pockets. i understand what you mean about ease of welding the left side, but with two solid pates you could just lay out rows of 7/32 holes through both plates at once and use those for welding from the outside. of course if your drilling by hand i can see your point. do you have a aluminum tool arm to use when welding?
 
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NC Biker said:
I agree with mike-E, why all the vertical pieces? I think you can simplify the design a great deal by having both sides one piece and having them extend up to provide the vertical support for your idler/tracking arm. and I would extend the right side to provide a mount for your motor. Take a look at the Wilmont 3 arm TAG grinder and follow Chris's lead.
Click to expand...

The right side actually is one piece with the motor mount.

I thought about extending the sides up to support the tension arm (I really like that style). I even have a version with it like that. But my local metal supply can only cut 1/4" bar stock and the widest they carry is 12". So I would have to get 1/4" plate cut from somewhere else to get anything tall enough which would also be much more expensive (I can't handle a full sheet..no room or enough muscle lol). I guess you can say my design is as much a side effect of function as it is ability to build.

And yeah...I've looked at quite a few tag-101 pictures! His grinder has been a real inspiration to me.
 
mike-E said:
just to add my two cents on the 5 pockets, you might find the bottom pocket useful.you could have a tool arm with some type of swiveling hook at the end that will hold a quench bucket that can be adjusted in and out. i would keep the pockets. i understand what you mean about ease of welding the left side, but with two solid pates you could just lay out rows of 7/32 holes through both plates at once and use those for welding from the outside. of course if your drilling by hand i can see your point. do you have a aluminum tool arm to use when welding?
Click to expand...

Oh man its like your reading my mind! That was an idea I had for that bottom pocket as well!

I'll give some more thought to double full plates - it might make it look cleaner even if I did grind the welds flush with the smaller plates.


And yep, tool arm in hand to be my weld guide - I ordered it when I got the wheels! Is .05" clearance about right? More?
 
..and I know some of you are thinking: why not just buy a Wilmont, etc.? Well, aside from cost...I enjoy the DIY aspect of things. It's about the journey, not just the destination for me. I'm sure some of you can relate.

Thanks for all the feedback so far! This is actually a build for my son, though I'll make heavy use of it as well until he moves off into his own place one day.
 
is that 50 thousands or 5? i wold shoot for .020 - .030 for horizontal and .010 - .015 vertical, this will be difficult without a mill though. i can definitely relate on the diy mindset. im sure you and your son will enjoy using this tool for years. please post pics when it's completed.
 
Actually getting the exact clearance would be easier when using multiple small plates fitting them one at a time. Using one large plate actually makes it harder since you have to cut the horizontal pieces precisely with no room for error. With the small plates you only have to get the height of the lock mounts approximate and can fill with weld as needed to get the precise fit (using sheet(s) of paper, etc as a shim while fitting up).

Regardless, here's a shot with a single plate. Not sure it's easier/better, but it would probably look cleaner in the finished product:

grinder2b_1plate_zpsfnrcgdxn.png
 
Javajaws, Since you already have the motor and it is a 1.5 hp you probably wont have a lot of power with doubling rpm and running a 5 inch drive wheel. You might consider running a jackshaft and pulleys like the KMG to double the speed and keep your power and also run a 4 inch drive wheel. I did this and had to sell my motor power to use the flat platen to flatten my blade blanks. I finally broke down and called an electrician to put in a 220 outlet and it solved many problems. Larry
 
Really? Everything I was reading said a 1750 rpm motor with the 2x on the vfd would have more torque than a native 3500 rpm motor. I'll see if I can dig up the link to the latest thread that talked about this. :(
 
I run a 1-1/2 hp 3ph 1750RPM motor with a KABC-27D set at 2X and a 5" drive wheel on a direct drive motor. This gives me around 4600 fpm belt speed on the top end. I have plenty of power and torque across the entire speed range and it works great for me.

I think I read every post here on this subject before deciding on a combination. There were lots of differing opinions on whether to use a 1750 or 3500 RPM motor, very confusing. In the end, I kept reading "get a 1750" every time Stacy would comment on the subject. That was my deciding factor and I'm glad I went that route. I have yet to see Stacy give bad advice on these forums. There's a reason he's the moderator here.
 
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