2x72" grinder help?

[petere76]

DC,

 

As an alternative suggestion to the variable speed motor and controler arrangement, try going with your basic 120220 V 1.5 HP motor and 2 matched step pulleys.  The speed range will obviously be fixed to the pulley sizing but the electronic control hassel you are experiencing will be eliminated. 

 

Ask yourself, do you really need the infinite adjustment of speed control you get from the fancy controller? if you do, the price will be the cost of a fabricated or purchased motor controller. If the cost outweighs the benifit, go with the pulley arrangement. The most expensive Baldor sander with variable HZ drive and the simplest home build sander with pulleys both grind metal very effectively. You are essentially balancing form, function and price against your needs and resources.  

 

No matter which way you choose to go, in the end you will have a great tool.  Good luck.

 

Peter

[Dan C]

I tore apart the treadmill and scavenged everything I could from it, including the board under the rolling track to use as attic flooring, wheels, nuts & bolts, and the steel frame.  Then I started looking closer at the digital controls of the TM and hooked it up.  It would take up a little more space, but functions as is and could be scaled down, unless you want cup holders and to take your pulse... 

 

Initially I was going to get a 120220 V 1.5 HP motor and 3 step pulleys until someone suggested this as an alternative.  At least this way all I'm missing now are various wheels, drive shafts and belts.

[Jim Deering]

G'day

 

I built a 2-in x 72-in belt grinder about twenty years ago from design drawings I'd prepared with the help of my best mate, who had ready access to a machine shop to deal with the large hollow shaft, which acts as the housing for the drive head, and the take-up pulley housing. The rest was cut from plate and hot rolled sections then welded together.

 

The contact wheels were commercial ones and ranged from Ø4-in to Ø13-in in plain face with an additional serrated face wheel of Ø8-in size. The durometer hardness of the wheels is 70, for those really interested. The take-up pulley was old stock from the company that made the contact wheels, crowned at Ø7-in. made from cast aluminium.

 

I looked at a few alternatives for contact wheels and decided the centripetal forces that would be generated at the rims of the larger contact wheels far exceeded the tensile capacity of things like wood, hence opting to obtain professionally-made ones. Don't underestimate the effect of a "home-made" contact wheel being out of balance either, especially large ones! This will be more of an issue if you are using variable speed drives, as you might inadvertently run a contact wheel that has been balanced at a specific speed at a speed where it is not balanced. With stepped pullies the speeds are fixed, in steps, so the likelihood of one being in the range where harmonics take over is reduced. The harmonics caused by an unbalance contact wheel can be quite surprising and even some heavier weight belts can get quite a bit of movement up between the contact wheel and take-up pulley at different speeds... But I digress into the infinite realm of details. Oops.

 

The grinder started off life with a 2HP AC motor and was fitted with 5-step pullies to give a reasonable range of speeds. The only time the stepped pullies were a nuisance was when the large diameter of the driven pulley interfered with longer blades. I knew this would be the case from the design phase, but at the time, buying a variable drive assembly was out of the question. There was however, a plan...

 

As I was making knives at the time, I found it was quite suitable for heavy stock removal and fine finishing, just by moving the belt to provide the required speeds. As an aside, if abrasive belts are run too slow, the grit breaks off the belt; too fast and the grit glazes, leading to lessened cutting and increased heating of the work-piece. The moral; know your grinding belt surface speeds for the given work-piece material and set your drive speeds to give the correct surface speed for the grinding belt.

 

Once the machine had generated some income, a 2HP DC Baldor motor was bought and mated to a speed controller. I turned a pair of microgroove pullies to accept a 5-ribbed belt and away I went with all the original features, plus variable control. The pullies were sized to provide clearance for the belt guard, which matched the drive head's outside diameter. This reduced the pulley to work-piece interference issue to zero.

 

Having now used that grinder over the interceding years, I would not hesitate to recommend variable speed for a belt grinder. I would recommend having that aim in mind from the start of the grinder's design though, then you can upgrade as your funds permit.

 

As for other sources to obtain variable motors, treadmills, some vacuum cleaners and ever large capacity drills can be used to provide motive force, with the requisite ingenuity necessary when it comes to mounting them into the grinder. Variable pitch pullies could even do the job, and they can be made from scratch, although that isn't a job for the inexperienced or under-equipped.

 

Pillow block bearings and precision ground shafting should take care of the rotating drive parts. Contact wheels experience quite small axial loading, from an engineering perspective, so collars to suit the shafting used could be used to hold the contact wheels in place. These can be obtained from engineering suppliers, and usually have two grub screws, which lock the collars into place on the shafting. If you are really operating on a shoestring, visit junk yards and look for old farm machinery. Use your imagination and you'll see the decrepit birth the new in your mind's eye.

 

The final words; get the electrical assembly done by a licensed electrician. No arguments! Make guards for the drive parts and shroud the belt as best you can while still permitting the access to the grinding belt you need to stop errant sparks getting in your eyes.

 

yad’G

[Scrap rat]

Everything mac, use 2" tubeing and 6005 sealed bearing and a 24 mm bolt to make your idler pulleys. Very light machining this way probabaly .020 id removal to accept the bearing and you will want a 1/32 taper from the center of the idler to the outside on the left and right side to make the belt track right! This is what i did and with the minimal stock removal its cheap to have turned on a lathe for you! McMaster Carr is a good place to get good prices if you are in the US! Good luck and im tearing apart my treadmill tomorrow haha thanks for the help guys

This is what i did

[Everything Mac]

Looking good guys.

[Dan C]

It's been awhile with multiple ongoing projects but I recently figured out the tracking on my 2x72 build, and am ready to mount the motor taken from a treadmill.  The tension arm came from a co-worker hatchback after he replaced the gas struts.

 

 

 

[VaughnT]

Very nice work, Dan.  Be ready for your design to be very loud, though.  All that tubing acts like acoustic chambers and will fire the sound straight into you as you work in front of it.  This gives you the bone-conduction as well as through-the-ear noise, so muffs will only help so much.

 

You can kill a lot of the noise by filling the voids with foam.  It turns the tubes into a solid mass, thus lowering the vibration frequency, and prevents bugs from making a home out of it.  Do a before-n-after and you'll definitely note a difference.

[Dan C]

I filled the tubing for the stand with sand and oil to add weight before sealing it. Hopefully that will help. I did the same thing when building my anvil stand. I did redo the arm today for the contact wheel using a solid piece of cold rolled square.