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High Speed Hand Piece

hi, great thread, thank you!


i spoke with grs regarding the 4:1 gear.

here are a few things i learned

it adds about an inch to the over length of the handpiece (he estimated approx 5.5-6” without, about 6.5-7” with)

it can be purchased and added by user later.

at it’s lowest rpms, it has more torque than a flexshaft, which needs to be at a mid/higher speed to build up torque (i hope i am saying that correctly…?)


Hi Julie,
Thanks for sharing this info…however, I’m not sure that GRS gave you a complete picture. You note:


at it’s lowest rpms, it has more torque than a flexshaft, which needs to be at a mid/higher speed to build up torque (i hope i am saying that correctly…?)


I think that this is true for the simplest Foredom with a rheostat controller. As speed goes down, so does torque on those models. However, there are geared down models which have a higher torque at low speeds…the motor has a 3:1 or 4:1 (I forget which) physically geared down speed…the top speed is lower, but the torque is higher. I think these are older models which may have now been phased out. However, there are also models which have a special solid state controller which boosts torque at low speeds. I don’t know specifically whether the grs micromotor has a higher torque than all the Foredoms and other flexshaft motors, but I’m just saying that Foredom dealt with the problem of low torque years ago in more than one way. Also, the older flexshaft models had a 1/6 hp motor…some still do, but some of the Foredoms now have a 1/3hp motor, which would also increase torque.

Unless these manufacturers can actually quote ft-lbs or nt-mt of torque figures to compare, I guess we’ll have to ask folks who have used both which is more powerful.

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Hi royjohn,

Thank you for the feedback! I wish I understood all this mechanical stuff better.

for me, the main draw of the micromotor is that I really like the thinner more flexible cords, as opposed to the stiffer flexshaft…

but…I also want a slim, short handpiece…this is my dilemma…the NSK handpieces seem too thick and long to me… and, the 4:1 reduction attachment would add about an inch more…

the foredom micromotor handpieces seem to be a bit shorter (to me(?), but still seem a bit thick…

I will probably just eventually get a slim, short foredom H.20 handpiece for my flexshaft…

foredom still makes the lower speed/ higher torque motors…
TX (1/3hp, max 15,000rpm), LX 1/10hp, max 5,000 rps)


Hi Julie and all,
The 4:1 ratio just means they are using gears to slow the motor down to 1/4 the max speed and that gives 4X the torque that would be available at any chosen speed if it were used without the gearing, in direct drive. The foredom flexshafts have a solid state controller on their motors. Instead of decreasing the voltage on both the field coils and the armature, it allows decreasing the voltage on one while leaving the other constant. This means that the speed changes, decreasing as the voltage goes down, but the torque, or pulling power of the motor remains the same. So you can use very slow speeds and not bog down. I hope that helps.

Now I have a question. As a setter, using burs to make holes in which to place diamonds and using burs to notch prongs, etc., wouldn’t I want slower rather than faster speeds? Or does a setter want a really fast tool? I thought the former was better for control…-royjohn

As I am also a long-time Diamond Setter, I use a slow rotating bur. I need to be ultra-careful in the cutting of the bus.
If the bur is cutting too fast, I might have little or no control over the metal cutting. Plus the fast rotating bur just might slip and the teeth will leave deep indentations in the metal.

“Gerry, on my iPhone”

Thanks, Gerry, I thought so…I learned about the bur going round and round the prong, “decorating” it, at the Hard Knocks School of Jewelry Creation…LOL…-royjohn

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This essay, that I just completed, is my 143rd tutorial-essay that gives you, the reader, an inside view on how diamonds are polished. In fact, the tools that are being shown are over 93 years old, but these tools are still being used today, as they were way back then.
I’ve used many photographs all through this essay. These will give you an insider’s view on how a diamond is actually polished.
Needless to say, this essay is quite an interesting view that not every jeweller has a chance to see. After writing this essay, I’m happy that you will have a greater understanding of this different kind of aspect of jewellery making.
I also showed you a pendant that I completed last week, using 239 diamonds. Without a diamond polisher, no piece of diamond jewellery can be made, it’s as simple as that.
Have a good read and learn a few things.

Hi Rob, on a related note…have you tried out any of these inside ring gravers to mark your items…?

from grs catalog


Julie…I have not. I am having enough trouble learning to control a straight graver. I really don’t need an inside graver as I do all my marking while a piece is flat. I have been experimenting to see how small I can engrave a legible number. Stay tuned. Thanks…Rob

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I have the now out of production Fordom 400k rpm turbine. That cat about $400 new. More recently I purchased a right angle 400K hand piece on ebay for $17.
The new hand piece works well and comes with 4 hook up tubes that connect the air water. The typical dental office set up includes a table that the hand piece connects to and separate foot pedals. To hook this type of had piece up on the cheap you need to find the right size tubing to connect the air. For the water you can use a cheap garden chemical sprayer. (we use warm water) Again finding the right sizes of tubing to reduce the air and water fittings is the hard part. We purchase all the 400k bits from LASCO. Made in the US. There are plenty of dental bits made in China as well. It does suck to use the wrong bit. If you get any bending you will have a fail.
The bits need to be designed and balanced for 400k. The bits are short for that reason.
As far as I know all the air turbines use the 1/16 or metric equal.

Diamond bits are often made by plaiting or sintering. Heat will ruin the bit quickly which is why a water spray is necessary.

One job that we often use the air turbine for is to make holes in stone beads bigger. Use a pointy bit and go around the inside edge of the hole in a circular fashion. You can get hurt. It might be less painful to make a jig to hold your work instead of holding it with your hand.

You might also use the air turbine to cut through layers of enamel. Then fill the cut marks with a different color and refire etc.
cheers marty

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