Can I convert bench grinder to flex shaft rotary?

[can20]

Hey everyone I’m just looking for advice. I have some pretty powerful bench grinders, and I am sick of all the underpowered rotary tools that I have been using. I just can’t find a good rotary tool with the power to not big down when I’m applying pressure to a work piece. So I am wondering, is there any sort of attachment that I can put on the spindle of a bench grinder that will basically convert it into a flex shaft rotary tool? I would love to use my 1hp grinder to power a handheld rotary tool. I’m imaging something that screws into the threaded spindle and has a long flexible piece and a handle that would work like a dremel tool. I’m looking online without much success. Does anyone know anything about this? I also have a drill press that I never use and would be ok with converting that, but it is certainly less powerful and I’m not sure how high the rpm will go on that, it’s the cheapest $100 Bauer drill press from harbor freight, and it’s not a great machine.
Thank you for any input, the knowledge that I receive from members of garage journal has been very valuable for me in my process of learning about tools and craftsmanship.

Cheers,
Chris

 

[john.k]

Yes ,but you will need a bit of engineering work ,such as a bracket to hold the outer jacket of the flex drive...............you could certainly drive the inner from the nut on one end of the grinder ...assuming its not RH and LH thread,which only bigger grinders are normally.

 

[RoninB4]

-What RPM do you want to work with? What sort of power/torque is needed? What types of work will this be put to use on? What immediately comes to mind is the flexible shaft rotary handpiece type from Foredom. These were the go-to used in all mold shops during the 80's and beyond. They were used all day long every day for grinding/polishing mold details. They were somewhat expensive, broke on a regular basis, had RPM that was suitable for small carbide burrs or polishing with diamond paste. They could be bogged by expecting them to take too big a "bite" and were limited to under 3/16" shank size. A Dremel is fairly anemic, a pneumatic pencil grinder has higher RPM. A pneumatic die grinder has a bit more power but all pneumatic tools make a lot of noise and ear muffs are essential indoors.

They did perform well for small detail work, if you're wanting to grind off excess weld slag then you'll need something else. Don't know if there's something that can adapt your bench grinder but checking RPM limits to the flexi-shaft AND what cutter/grinding wheel goes on the handpiece needs to be verified.

 

[neophyte]

Flex shaft attachments for other tools usually cost almost as much as buying a complete Foredom unit.
Metabo makes one, and it costs $350+.

Have you tried a Foredom unit, or one if the lower speed, higher torque Foredom motors?

There are also larger “Industrial Strength” flex shaft units, Suhner is one manufacturer, but price usually is in the thousands of dollars.

Converting a grinder might be possible, but usually the outer flex shaft housing is fixed to the grinder.

 

[neophyte]

Terrco is the US manufacturer.

Terrco Inc | Flex-shaft

 

[shoot summ]

Flex shaft attachments for other tools usually cost almost as much as buying a complete Foredom unit.
Metabo makes one, and it costs $350+.

Have you tried a Foredom unit, or one if the lower speed, higher torque Foredom motors?

There are also larger “Industrial Strength” flex shaft units, Suhner is one manufacturer, but price usually is in the thousands of dollars.

Converting a grinder might be possible, but usually the outer flex shaft housing is fixed to the grinder.

I have a Foredom, great machine, I can't imagine trying to rig a bench grinder to get a similar result. Foot control and variable speed are huge benefits to the Foredom, plus the flexibility of not having a bench grinder that you would have to make room for.

Dad had an old school flex shaft machine years ago, basically a large electric motor with a flex shaft. I used it to clean up the frame on a '50 Studebaker truck he was building. It would get busy, one speed, the wire wheels he had were brutal, I had a lot of the wires stuck in me while I was doing it.

ETA looks like there is an import bench grinder available with a flex shaft from HF and many other chicom dealers.

 

[seber]

Foredom is the classic answer but heavy duty types are available if you are willing to spend the money.

Industrial Flexible Shaft #5 - 5 Foot

caswellplating.com

 

[can20]

-What RPM do you want to work with? What sort of power/torque is needed? What types of work will this be put to use on? What immediately comes to mind is the flexible shaft rotary handpiece type from Foredom. These were the go-to used in all mold shops during the 80's and beyond. They were used all day long every day for grinding/polishing mold details. They were somewhat expensive, broke on a regular basis, had RPM that was suitable for small carbide burrs or polishing with diamond paste. They could be bogged by expecting them to take too big a "bite" and were limited to under 3/16" shank size. A Dremel is fairly anemic, a pneumatic pencil grinder has higher RPM. A pneumatic die grinder has a bit more power but all pneumatic tools make a lot of noise and ear muffs are essential indoors.

They did perform well for small detail work, if you're wanting to grind off excess weld slag then you'll need something else. Don't know if there's something that can adapt your bench grinder but checking RPM limits to the flexi-shaft AND what cutter/grinding wheel goes on the handpiece needs to be verified.

I want a rotary tool for basic grinding, sanding, rust/paint stripping, and polishing for restoration of bench vises and old farm tools/equipment. I have just found that the tools I’ve tried bog down very easily. I have a bad back and standing at a bench grinder/buffer irritates me and I like to sit in the corner of my workshop and work on my projects. I’m new to tools and to the hobby. Also, I’m experimenting and trying hard to figure out the methods and the commercially available products that will allow me to produce an impressive mirror finish on steel and iron for my projects restoring bench vises and other old tools. I would also very much appreciate any advice when it comes to that goal: tools, consumables, techniques and tips. I am truly new to learning about tools—I’m a pharmacist by trade and grew up in a white collar family. Even if you think it is very basic advice, it will likely help me build my knowledge and bring me some joy as I achieve greater results in my hobby.

 

[can20]

T

Foredom is the classic answer but heavy duty types are available if you are willing to spend the money.

Industrial Flexible Shaft #5 - 5 Foot

caswellplating.com

Thank you, that looks like exactly what I was thinking. But I had no idea it would be that price, in my mind it was just something that screwed onto a bench grinder and allowed the powerful motor to power a rotary handheld tool. At that price, maybe it would be better to buy one of those units 1000w or 780w with the hanging motor attached to a flex shaft and foot pedal for maybe $100-150? I’m not sure, what do you think? Converting a bench grinder or just buying a rotary carving unit. Again, if you know good products that might accomplish this without involving a bench grinder, I also app that advice.
Cheers

 

[neophyte]

Handheld electric die grinders are available, and are usually fairly powerful.
Coat can vary from $80 for a Harbor Freight Hercules model,
To $150-$350 for a Dewalt model, depending on whether you want an older brushed, or newer brushless model.
Most major Power tool manufacturers manufacture similar die grinders, ie. Bosch, Makita, Hitachi (Now Metabo HPT), Fein, etc.
electric units aren’t going to be as small as a pneumatic (air driven) die grinder, but for the pneumatic die grinder, you would need a large compressor to supply continuous air.

Corded die grinders usually come in two speed ranges.
Units with a max speed around 30,000rpm.
(Variable speed version usually are around 10,000rpm to 30,000rpm)
And units with a max speed of around 8,000rpm. (For variable speed version, maybe 2,500rpm-8,000tpm).
The higher speed version are usually made for 2” and under accessories.
The lower speed versions for maybe up to 4” diameter accessories, although you need to check the accessories, and only use accessories rated for more than the maximum rpm rating of the tool.
Fixed speed brushed electric die grinders can be used at lower speed using a router speed controller, if you want ti find an older used model to save money.

The flex shaft attachments for motors you may already have, used yo be a thing a few decades ago, but are much harder to find nowadays, and much more expensive.
Used units might be available on ebay if you know what to look for, but finding all the hand pieces and attachments might be a problem.
Suhner, which I mentioned above, does sell components piecemeal, but it’s way cheaper to purchase a complete kit with a variety of different tool ends, and the cost is still thousands of dollars. (Used units show up on ebay, but are usually missing pieces)

For smaller “Dremel sized” work, Foredom is basically considered the “Industrial” duty option.
Dumore, is another Industrial US manufacturer of smaller industrial flex shaft tools, and hand held electric die grinders.
There are also plenty of Chines knockoffs on the older Foredom designs, if you need to spend a bit less.
I doubt the knock offs are the same quality, but plenty of people find the units usable.

 

[RoninB4]

I want a rotary tool for basic grinding, sanding, rust/paint stripping, and polishing for restoration of bench vises and old farm tools/equipment.

-That will indeed require a moto-tool with some "grunt" to accomplish the task and some good breathing filtration to prevent the metal particles entering your lungs, I'm not exaggerating about the need for filtering the air you'll breathe. Put a spotlight over the area you're working on and you can see all the particles hanging in the air. This will occur whether grinding, sanding, or polishing. Do NOT overlook this for your own safety. The effect it can have on your lungs can be considerable and serious.

I have just found that the tools I’ve tried bog down very easily.

-To be expected with hobby grade tools. Some will work ok if you work within the limits of the tool, most are just a time consuming exercise for the very reason you've mentioned, lack of power/torque. I expect you'll have to have more than ONE moto-tool that's capable of either torque or RPM for reasons I'll go into. Time is money when doing more than an occasional project. The faster, more capable tools are industrial grade and costs go all the way to absurd. You'll have to estimate what your time/effort is worth.

I’m experimenting and trying hard to figure out the methods and the commercially available products that will allow me to produce an impressive mirror finish on steel and iron for my projects restoring bench vises and other old tools.

-This is where there's a difference. Removing rust or just shaping the metal (defining surface shapes) call for all the "grunt" your tool can deliver as you lean into/onto the work trying to get below the unacceptable surface (rust, casting slag, etc.). Castings also exhibit the deteriorating production condition of the casting mold itself. All the small lumps, ribs, mismatch, sprue remains, and crappy surface finishes need metal removal. A moto-tool like a Dremel just isn't up to the task. A Dremel is ok for working on small details the size of a salad crouton (or a pair of dice) but anything larger is an endurance event IMO.

Polishing is a different animal than grinding/shaping/sanding. Polishing is making surface scratches in an ever diminishing process. The size (width and depth) of those scratches will determine the surface finish. It's relatively easy to produce a "shiny" surface on most metals. Surface finish is defined by roughness, waviness, and predominant pattern. Creating a truly mirror surface is more involved and with some metals can be difficult. Polishing is where friction is important and that calls for RPM as you're only removing a tiny amount of metal from the surface. The correct abrasive medium allows you to cut instead of just smear the metal surface. You'll work in abrasive grit (size of abrasive particles) that's held in a buffing wheel, rubberized wheel, or sanding belt/drum from 32-400 grit in stages to produce finer scratch marks. That can/will produce "shiny" surfaces where you can see the previous grit scratches. For a truly mirror surface it will take much more. Part of my daily duties on the job was create a truly mirror surface on some mold/die surface and that called for using diamond compound, a felt bob, and a moto-tool capable of relatively high RPM after I'd worked up through the grit sizes. It's also not just a simple matter of "massaging" the surface. As you approach mirror finish any deviation from the geometrical shape (round or flat) becomes quite noticeable as a difference in the reflective appearance (wavy, concave/convex, "potholes", casting occlusions, etc.). Sometimes the metal will just simply smear and leave a dull gray appearance. Do some reading on surface finish, bypass a lot of the technical symbols and callouts to obtain info you really need. The chart below is a visual shorthand for a deep subject you don't need all of.

I would also very much appreciate any advice when it comes to that goal: tools, consumables, techniques and tips. I am truly new to learning about tools—

-I can probably tell you a lot more than this post but it can be lengthy and probably boring for others. Contact me off list for more information than most normal people would ever want to know. I don't mind, I'm retired now.

I’m a pharmacist by trade and grew up in a white collar family. Even if you think it is very basic advice, it will likely help me build my knowledge and bring me some joy as I achieve greater results in my hobby.

-Interesting, I was a pharmacy spec in the military but washed out of college pharmacy school trying to keep a roof over my head for 5 years. Ran out of money and motivation. I might have finished if I didn't want to eat and stay warm. Maybe I wasn't smart enough either. Found employment in a machine shop during the summer and never returned to school. Machine shop work was dirty and dangerous but at least it kept me out of the higher tax brackets.

My apologies to the collective for being long winded on this subject.

 

[RTM]

For a truly mirror surface it will take much more. Part of my daily duties on the job was create a truly mirror surface on some mold/die surface and that called for using diamond compound, a felt bob, and a moto-tool capable of relatively high RPM after I'd worked up through the grit sizes. It's also not just a simple matter of "massaging" the surface. As you approach mirror finish any deviation from the geometrical shape (round or flat) becomes quite noticeable as a difference in the reflective appearance (wavy, concave/convex, "potholes", casting occlusions, etc.).

I’ve managed to get plane blades up to mirror finish, stepping up from 320 to 2000 grit wet dry paper. I personally would not want to try on something like a bench vise or wrench, my time is worth much more than that, for all the reasons noted above.

 

[RoninB4]

I’ve managed to get plane blades up to mirror finish, stepping up from 320 to 2000 grit wet dry paper. I personally would not want to try on something like a bench vise or wrench, my time is worth much more than that, for all the reasons noted above.

-I expect that you probably did achieve a mirror-like surface finish on a plane blade without resorting to grit size beyond 2000 or diamond polish for that matter. Part of that is because the plane blade is a type of tool steel and easier to achieve a better finish. The other reason is because of the blade shape. It's already got two planar surfaces to reference, no flattening required. I read once that single edge wood working tools (plane blades/sole, chisels, etc.) benefit from an improved surface as there's less friction for the base wood/shavings to drag on. I tried it on one of my chisels and it seemed to make a difference.

My own personal vises (except the precision grinding vises) are only cleaned up a bit and a rattle can paint job. I like to leave the dings and casting flaws alone as the history of the vise. I've got a #10 Prentis and a #32 Reed that are both 100 years old. I wanted to duplicate the factory finish (Japanning) but ended up with rattle can paint. Putting a mirror finish on a casting is for more energetic sorts than I am.

 

[driftpin]

I have a Sears belt/disc sander which also accepts a flex shaft drive. I don't have the flex shaft drive for it.

 

[can20]

Handheld electric die grinders are available, and are usually fairly powerful.
Coat can vary from $80 for a Harbor Freight Hercules model,
To $150-$350 for a Dewalt model, depending on whether you want an older brushed, or newer brushless model.
Most major Power tool manufacturers manufacture similar die grinders, ie. Bosch, Makita, Hitachi (Now Metabo HPT), Fein, etc.
electric units aren’t going to be as small as a pneumatic (air driven) die grinder, but for the pneumatic die grinder, you would need a large compressor to supply continuous air.

Corded die grinders usually come in two speed ranges.
Units with a max speed around 30,000rpm.
(Variable speed version usually are around 10,000rpm to 30,000rpm)
And units with a max speed of around 8,000rpm. (For variable speed version, maybe 2,500rpm-8,000tpm).
The higher speed version are usually made for 2” and under accessories.
The lower speed versions for maybe up to 4” diameter accessories, although you need to check the accessories, and only use accessories rated for more than the maximum rpm rating of the tool.
Fixed speed brushed electric die grinders can be used at lower speed using a router speed controller, if you want ti find an older used model to save money.

The flex shaft attachments for motors you may already have, used yo be a thing a few decades ago, but are much harder to find nowadays, and much more expensive.
Used units might be available on ebay if you know what to look for, but finding all the hand pieces and attachments might be a problem.
Suhner, which I mentioned above, does sell components piecemeal, but it’s way cheaper to purchase a complete kit with a variety of different tool ends, and the cost is still thousands of dollars. (Used units show up on ebay, but are usually missing pieces)

For smaller “Dremel sized” work, Foredom is basically considered the “Industrial” duty option.
Dumore, is another Industrial US manufacturer of smaller industrial flex shaft tools, and hand held electric die grinders.
There are also plenty of Chines knockoffs on the older Foredom designs, if you need to spend a bit less.
I doubt the knock offs are the same quality, but plenty of people find the units usable.

I want to thank you for sharing this advice with me. I am looking at some die grinders now and am realizing that this would be a great tool for me to have, for my playing around in the garage and hobbying. If I could also use it to spin some of my dremel type attachments easily then that would be great for me. Thanks.

 

[neophyte]

I want to thank you for sharing this advice with me. I am looking at some die grinders now and am realizing that this would be a great tool for me to have, for my playing around in the garage and hobbying. If I could also use it to spin some of my dremel type attachments easily then that would be great for me. Thanks.

Collet sizes for die grinders are usually 1/8” and 1/4” for the USA, and 3mm, 6mm, and sometimes 8mm in Europe.
Dremel accessories usually have smaller shanks, but collet reducers are available to let you run smaller shank diameters in larger collets.
Check eBay or router bit suppliers, or sometimes model making suppliers, since model makers like yo use smaller bits in larger better routers.

 

[cherrybomb]

Check the Lee Valley site,they have a rotary cable.I use mine in my drill press.Great quality