BGM 100 slow speed vs high speed grinder

[Blake]

Sorry if there is a thread on this specifically, searched but do not see one close. I am thinking of getting a BGM100 so I do not have to do the heavy metal reshaping on the Tormek. I already have a high speed grinder. Have considered getting a slow speed (1750 rpm) but am wondering if I can get the results on the high speed and if I am careful avoid the overheating issue. once the tools are in the right shape I should be on the Tormek anyway. If I can use my existing grinder (it is 6" not 8" but what I read says that is do-able), I would probably pull the trigger on that faster than if I have to get a third grinder. Anyone dealt with this issue? 

[grepper]

Yes.  A lot of people use it for exactly that.  Just be careful, like you say, of heat.  As Tormek says here:
http://tormek.com/international/en/accessories/other-accessories/bgm-100-bench-grinder-mounting-set/
"However, there is no secret that when it comes to wood turning tools the initial shaping can be done faster on a bench grinder."

You might want to consider getting a CBN wheel for your bench grinder.   They don't generate much heat.

[Ken S]

Blake,

I would not advise purchasing a second dry grinder. If you calculate the surface feet per  minute ( circumference times RPM), you will find not much difference between a six inch high speed grinder and an eight inch low speed grinder.

I would have two related suggestions for you. 1) Use a forty six grit Norton 3X wheel on your dry grinder. The coarse grit helps it run cooler. You presumably already have a Tormek for the finish grinding. The forty six grit wheel will remove a lot of metal and leave a surprisingly smooth finish. I have posted a simple method of adapting the bore diameter of the Norton wheels to the 12mm bore of the Tormek.

2) Get the same 3x wheel in the eight inch diameter and use it on your  Tormek. I ground away on a HSS metal lathe bit for five minutes continuously with the 46 grit wheel on the Tormek (wet grinding, just like a Tormek wheel) with  my fingers quite close to the grinding and my fingers did not even get warm. While this may notbe quite as fast as using a high speed dry grinder, it is much faster than using either of the Tormek wheels. You will probably want a final fine grind with the SG wheel.

Have you tried reshaping with the Tormek? I would first be sure from first hand testing that you find the reshaping too time consuming before trying anything else.

A CBN wheel for your Tormekwould be theCadillac solution.

Ken

[Blake]

Thank both of you for the feedback. I think I will order the BGM100 and a new aluminum oxide wheel for my 6" old standard grinder. Will take your suggestion on the Norton 46. Unless the heat generation is a lot greater on the lower grit. Originally I was thinking 60. The CBN is just too expensive for me to justify, especially after the T-7, woodworking kit, wood turners kit... You know the drill.
On grinding on the Tormek, I have done quite a bit because many of my tools required initial reshaping, and that has primarily been knives, hand tools garden equipment. I am just starting my turning tools which I sharpened without jigs on the dry grinder, the are fairly sharp but not accurate on true shape. So I know there will be a lot of reshaping. I am less concerned with tome than wear on the grindstone of the T-7. Heavy metal removal seems to cause me to true the stone more often. I think I would rather use the stone for what it excels at. I have only had the rig since early May and I am down to 237 mm on the stone. Still fine and lots to go of course but my sense is to do the beefy stuff on a dry grinder, especially if I can use the one I already have.

[Ken S]

Blake,

I believe conventional wisdom is that coarser grinding wheels run cooler than finer wheels. I have used the 46 grit 3X on my dry grinder for several years, and like it. (My other wheel is an 80 grit "white wheel", which I have not used since getting the Tormek.)
Norton makes the 3X wheels in two different hardnesses, I believe I and K, if memory serves. The K (or letter furthest from A) is the harder, and that is the one I have. I like it, although I have not tried the other hardness, so I really cannot comment on it.

I have used both the 46 and 80 grit 3X wheels (wet) on the Tormek. My initial conclusion is that either one would suffice, although in my test, the 46 grit ground away as much HSS in four minutes that the 80 grit did in five.

You definitely sound like someone who does enough heavy work to need something beyond the Tormek wheels. The 3X on your dry grinder should get the job done for you without a lot of expense. I would suggest doing most of the shaping with the dry grinder, and leaving the last fine edge stuff to the Tormek's cool wet grinding.

Please keep us posted.

Ken