slight wobble with my grinder

[Matt Mackinnon]

I bought a set of CBN wheels from Dave (DWay) so I am pretty sure that both the wheels I got are not the problem as they both wobble equally The grinder I got used when I bought my lathe, so to be totally honest, i don't know how true it ran in the beginning. The grinder had a set of balanced oneway wheels on it before, and running it looked to be fine, but those wheels don't have a flat sharp edge to really see.

I am not sure how to post video, but at a slower speed (when the grinder is slowing down) you can see a noticeable wobble in the wheel. When it gets up to speed, it looks to be flat. I haven't tried using them yet as I thought it better to ask questions first. Should the grinding wheel be flat and true all the time, or is it like a lathe, where are when you increase the speed, it can balance out a standing wave and straighten itself out.

Or would you say that the grinding wheel is shot, and best to simply buy a new one. Heck, I've just spent $400+ on new CBN wheels, if that means a new grinder then so be it.

[Jon Prouty]

I would try getting one wheel balanced by rotating it on the DWay bushing and tightening it down. Leave the other one off while doing this. It takes some fiddling and effort - it took me about 30 minutes until I was satisfied and got a good result. Once you got one side good, do the other being sure not to mess up the first one in the process. Good luck!

[Reed Gray]

Well, first, take the wheels off and turn the grinder on and see if there is any wobble to the shafts on the grinder. Then mount a wheel first on one side, and then second on the other side. Dave's wheels come spin and bubble balanced, so most likely are not the problem.

I do have the Baldor grinders, which are very solid, and run as true as humanly possible. I have Dave's wheels, as well as one Optigrind, and one of the Cuttermaster wheels. I have to space them out about 5/8 inch from the grinder motor housing because there is a pin on the shaft for the flanges that come with the grinder, but those flanges only work with the solid flat wheels. I first used the stamped washers from the big box store. All 3 wheels had noticeable side wobble when starting up. There was no wobble on the surface of the wheel. When the wheels all came up to full speed, they all ran true enough so that the side grind option could be used no problem. Stamped washers = bad, just like plastic bushings. Weight of the wheels seems to be high/heavy enough so that when they are up to speed, they can over come most of the wobble caused in my case by cheap washers, and maybe in your case by a motor shaft that has some run out in it. I did go to a machine shop and have some machined washers made and that solved the run out at slow speeds. They did run a bit better for the side ways wobble as well. Note here, you do not want to over tighten your grinding wheels.

robo hippy

[Thom Sturgill]

Sounds like you've gotten good advise here. I remember reading one tool vendor say a few years ago that he had never had a bod grinder, it was always the wheels that caused the problem, and before CBN wheels it most likely was the wheel and the manufacturing technology.

The new CBN wheels make me wonder if he would take that back today. I think we as turners will start demanding better grinders. After all why put $400 worth of wheels on a $100 grinder that wobbles even if you can tweak most of it out. Unfortunately, better grinders go up in price quickly, with 8" Baldor industrial grinders coming in near $1000.

[Josh Bowman]

Got to ask a dumb question here. Do you have the correct Dway bushing installed??

[David C. Roseman]

Matt, in addition to Jon's and Reed's suggestions, I'd also be alert to a possible bushing issue, since you hadn't noticed any runout with the Oneway wheels on the same grinder. It's very unlikely to be the D-Way CBN wheels themselves, given their quality and precision balancing. Plus, you're noticing the same runout with both wheels. I assume you're using the machined bushings that D-Way recommends for your grinder? I had a similar problem recently with a new CBN wheel on a fairly new (and inexpensive) Woodcraft slow-speed grinder. The grinder had been running very true with the original aluminum oxide wheels, after I adjusted the wheels in 1/8th turn (45 degree) increments per Woodcraft's updated instructions. I put a new D-Way CBN wheel and machined bushing on one side expecting to be dazzled and got noticeable wobble at start-up and wind-down, no matter how much I fiddled with adjustments. :eek:

Turned out to be nothing more than a bushing issue. The counter-bore in the bushing intended to allow it to extend a few millimeters over the unthreaded shoulder of the short shaft of that particular grinder was not seating properly. Dave Schweitzer at D-Way got me sorted right out.

So, if you still have the wobble after following the steps Jon and Reed suggest, I'd next focus on the bushings, and their fit on the shafts of your particular grinder. Doubt it's the grinder that's causing the problem. There's not much simpler than a bench grinder, it's just a double-shafted motor. The CBN wheels with the right bushings can make an inexpensive one into a very sweet machine.

David

[Matt Mackinnon]

I started of with the two washers on the inside that came with the unit. Dave shipped the wheels with a washer, so I put that in first, then the other washers on the outside. Then I took the guards off completely so not washers were needed at all (as no guard to rub).

I have not tried it with only a single wheel, and I will give it a go with a black sharpie and seeing if rotating the wheel location on Dave's bushings, as well as the bushings to the shaft makes any difference. But from the sounds of it, this isn't uncommon, and it's not a simple answer of "oh that's a defective grinder, and replacing it will solve the problem out the box".

Thanks.

Matt

[David C. Roseman]

Matt, further to my earlier post, I should have added that, even with the wobble at start-up and wind-down due to the bushing issue, the CBN wheel ground my gouges beautifully once up to speed. I really wasn't able to tell a difference in actual grinding performance after sorting out the bushing issue. I agree with your idea that at higher rpm the eight-pound wheel may be balancing out the standing wave somewhat. I think it's also due to the fact that even with a Oneway Wolverine grinding jig, grinding gouges isn't exactly a precision machining operation, at least for me. :) If you ultimately end up still having a slight wobble at start-up and wind-down, I don't think that alone is worth replacing the grinder for. JMHO.

David

[Matt Mackinnon]

The problem is most definitely the bench grinder. After spending an hour slowly rotating the wheel on the sleeve, and the sleeve on the shaft in hopes of reducing the slow speed wobble, I determined that the left side of the grinder is not nearly as straight as the right hand side of the grinder. But after talking with Dave, and just cranking it up to speed, and putting a tool to the CBN, it cuts like there is no problem, and the wheels seem pretty stable at 1750 rpm. So I don't see and reason not to just use it as is.

I have glued up some new particle board to lift the grinder up 1.5" to get it closer to what Oneway would like according to the manual. And tomorrow after the glue has cured, I can drill out my holes to bolt it all together and get some sharp tools going for me.

Thanks for all the help (and hand holding). Coming from an engineering background where you cut items to +- 0.0005", the art of woodturning is a whole new mind set to get use to.

Matt.

[Matt Mackinnon]

Rather than start another thread, I hope that this gets read. Does everyone keep the wheel guards on their grinder once they moved over to CBN? As the new wheels will never explode, it's not that you need a guard to protect you from that, but it does keep you somewhat protected from accidental touching the spinning wheel once you walk away from the grinder and are not paying total attention to it. Lets face it those wheels keep spinning for quite some time.

I know from Dave's videos that he has taken his off. But what do the rest of the Creek do?

[Josh Bowman]

I took mine off, it got kind of in the way.

[David C. Roseman]

I took mine off, it got kind of in the way.

Ditto for me. With the Woodcraft grinder (and probably some other makes out there), there was not enough room for the guard and the wide wheel. I think D-Way mentions this on the web site. Don't miss the guard a bit.

David

[Russell Neyman]

Funny thing is I discussed this with Dave Sweitzer just last night. He confirms that it's just sloppy tooling on the grinder shaft and that a sleeve will resolve the issue.