View Full Version : Bizarre Sander roll accident

02-06-2014, 02:44 PM
Let me start by saying I am typing this one handed!
So, I use the sander rolls loads, and have done for years with no problems. Today, I was sanding the edge of a simple pendant piece (no weird sticky out bits etc). I was holding the metal in my right hand, fortiflex handpiece in my left (am left handed). As always, I had on goggles and had secured the chuck with the little spanner so it was super tight.
Whilst sanding away, I felt the roll do something big and catchy (unclear what, it all happened very, very fast) so immediately take my foot off the pedal. I still had the pendant in my hand, it is fine silver, and wasn't bent or anything, so that couldn't have experienced huge force. However, the sander roll itself had completely come off the spindle, and the spindle itself was bent at right angles! It had pulled free of the handpiece, so I don't know if it had hit the (concrete) floor and bent, or bent when the incident happened. The roll itself had launched itself and twisted into my t-shirt where it had torn a great big bloody hole.
After I'd let the dust settle and had started breathing again (something had made a big noise and everything seemed to fly everywhere at once!), I cautiously ran the dremel again. It seemed a tiny bit grindy, but after a few seconds seemed fine. However, I noticed lots of oil on my hand, and the handpiece seemed to be unscrewing partway up (in a place I don't believei t should!) I've tightened it back up, but it now does seem to come loose very easily. I've attached a pic pointing to the part I'm talking about. Do you think it will be safe to use? Like I say, it feels ok, but I don't want anything falling apart during high speed use!
Irrelevant to products, but I've really hurt my hand, my third finger particularly - can't bend it, (no idea how as that one wasn't holding anything) and my shoulder is in agony (I'm certainly not going to be doing any more making this week :-( )
I then had to have the joy of walking to the bus to come home with gaffa tape holding my t-shirt together so the world was spared my boobs.
The picture shows an unused sander and the roll and spindle that caused the excitement, and the bit of silver I was using.
Any ideas please?

02-06-2014, 03:14 PM
Ouch Lydia - can't offer much advice on mechanical problems, but sending lots of sympathy. The finger may be dislocated if you can't bend it - trip to the doctors or minor injuries unit sounds in order to me.

Wishing you a speedy recovery, Susie.

02-06-2014, 03:23 PM
Ouch! :( Hope your finger recovers quickly!


02-06-2014, 03:24 PM
Yes Lydia, that is a well known hazard with sanding rolls because the rolls are heavy and the spindles very long. At a certain speed, and now you have an idea how fast, centrifugal force takes over and causes the spindle to bend outwards giving you a fright. I'm sorry you hurt your hand and wrenched your back jumping away.

I certainly hope that you will soon recover, but don't blame your handpiece. If it does up properly and runs smoothly it should be alright. If not it will need servicing, because it has been damaged.

For the future, take care to use only moderate speeds and if you have a separating disk cut the spindle a few mm shorter to reduce the force on it. Dennis.

02-06-2014, 03:28 PM
Similarly, ouch, sympathy and get it checked over.

What I suspect has probably happened - the sanding roll has possibly worked slightly loose (can't remember - Jacobs chuck on yours?), has had some off-axis force at high speed which started it spinning out-of-balance which then gets much worse very, very quickly. I've done it with felt mops in the past but nothing with much mass to it. Once these things propeller themselves, they flail around with a lot of force.

How fast were you running it when it went, and was the shank completely buried in the chuck? I usually modify my sanding mandrels by cutting the shank down; I don't run them over around 10krpm.

02-06-2014, 03:29 PM
I could have saved myself some typing there, Dennis!

02-06-2014, 05:03 PM
that sounds likely. (The length/axis/resulting carnage I mean). I never put them with the whole shank down inside the chuck as (ironically) I find if the gluey bit at the top of the spindle is in in the chuck, it often means it can loosen during use. I didn't think it was the hand piece at fault, just wondered if it is likely to be in trouble since it's happened. I realise that's a bit of an unanswerable question without looking at it :-S
There's no accurate way of measuring the speed it's going, but I was giving it some welly Peter! (was almost flat out)
Hopefully won't happen again! Thanks for the tips and wishes!

02-06-2014, 05:17 PM
Your Dremel has a top speed of 20k, I'll need to do some googling to find the max speed for the rolls - but for larger diameter, heavier accessories I'll always run them slower. Rubber wheels I don't run at more than 10k, for example. Some of them will give you some warning that they're being run too fast with excessive vibration but in that case I don't think you'd have had much before it failed.

Dare I ask where the sanding roll was made?

02-06-2014, 05:22 PM
Sorry too to hear about your nasty incident. It's probably a bit early to tell but hopefully your injuries won't have any lasting effects.

It looks like what you've experienced is an extreme case of kickback after the sander roll has snagged on something. There may be something in the Dremel manual advising about kickback. All that rotational force has suddenly met with a dead stop and has had to dissipate itself in some way - in your case by simultaneously twisting the head off the tool, spitting it out of the handpiece and throwing it at you violently.

The oil coming out of the handpiece may be a sign of a leaking bearing race (I'm assuming it has them) or it may just be the grease that lubricates the flexshaft that has somehow managed to get out. You could do with having a look inside. Have a look at your manual and see how you unscrew the casing of the handpiece to have a look inside. If you are getting a rough sound or the handpiece gets abnormally warm in use then there may have been some damage done to the bearings.

Hope you feel a bit better tomorrow.

02-06-2014, 05:25 PM
I've been using those roll sanders for years and have never had a problem with them. Hope you recover quickly.

02-06-2014, 06:36 PM
Thanks all. Think I am so used to much slower machines - have used these rolls for years and I suppose I have not adjusted my speeds accordingly, and need to take it down a notch or ten.
It looks like the flexshaft grease, will open it up tomorrow. Mightily annoyed with myself. My arm is screaming from shoulder to fingertip so am going to mainline ibuprofen and hope I don't manage to cause anything to explode or do anything else exciting tomorrow!