die grinder technique

I, unfortunately, occasionally put a hole in the wrong place and need to slot it, or need some extra clearance. I usually use a die grinder to remove the offending metal. I use a 3/8" double cut carbide bur, and the material is structural steel. My question for the experts is on proper technique. I find that the bur skips, making the tool jump around and dinging up everything around it. It seems to happen fairly randomly. I can be in the cut for quite a while one time before it starts skipping, the next time it will skip immediately. Adding a squirt of cutting fluid seems to maybe help a little bit, but it could be the placebo effect.

Is there some better technique for doing this? Tips and tricks?

This is basically the burr I'm using McMaster-Carr

Thanks,
Daniel

It’s like kickback on a chainsaw. Mostly happens when you let the leading edge of the burr get too far forward in the cut and too much pressure.
Try anchoring your lead hand against the work (so you have good leverage on the back end of the grinder to control the cut) and do your best to keep the burr towards the back side of the cut any time you’re pushing down with any pressure.

My experience has been to either push hard and not let it move or go very lightly.

I find it impossible to control completely. I get the best results by 'feathering' the air valve on the grinder because often a (much) slower speed and torque is helpful. Unfortunately, few die grinders are easy to control without additional components, but I just stick the middle finger under the lever and sort of do a push-pull to control it. A bit like a two-hand grip on a pistol. Its a little awkward and not a perfect solution but it helps. An iron-fisted grip on the grinder with both hands is also essential.

Thanks, that helped a bit. I think I'm also going to need more practice.

All else being equal, is a larger or a smaller bur going to kick back more?

Larger is worse in a slot if it fits too close to the sides. Half to 2/3 slot width is good and it helps greatly to move the cutter like a knife, down the straight sides and smoothly into the bottom curve of the slot, taking nothing off the sides until you get into the bottom radius. Also, you move in the direction against the rotation of the cutter. Fine-cut burrs have less tendency to run away, but cut slower and clogs are harder to clear.

Do more prep work to reduce errors

Invest in layout tools

Work from a print

Do your own CAD, Draftsight is easy to use and cost $100 a year. Use CAD to dimension your cut outs X, Y from a point on your work

Heat the workshop

Wear warm clothes

Don't forget to wear safety glasses

Think of it as a "wiping" motion ,not a plunging motion.

petersen said:

Think of it as a "wiping" motion ,not a plunging motion.

Click to expand...

I seem to have pretty good luck using a sweeping motion in a climb mill direction.

Very interesting replies. Like a lot of hand tool use, I think a lot of it has to do with individual technique. A combination of personal factors work together (or against each other).

Thinking about what works for me, and combining what a few have advised, I'd say if swiping in the direction of the cutter (climb cutting), lighter pressure like Johnfalco's sweep. If swiping against the direction of the cutter (conventional cutting) then really choking-up on the grinder and anchoring your forward hand on the workpiece so you've got a really solid control of the tip.

You can move in either direction easily (climb or conventional) as long as you have a good solid grip on the grinder. Absolutely do not attempt stock removal one handed - that is just asking for trouble and broken burrs. And number one consideration is to use a burr that is considerably smaller in diameter than the width of the slot or hole. I like 1/2 the width or even smaller if possible. Double cut for sure. I like to make short, somewhat deep cuts so the burr has a chance to keep cool Try not to keep it buried the whole time or you'll just dull the burr.

If the tool is grabbing and skipping and jumping its way around the hole you either aren't gripping it solidly enough or your burr diameter is too close to the hole/slot width. I tend to use climb cuts to rough-in so that the burr isn't pulled into and past the finished edge. Conventional or climb for final shaping and smoothing. Layout is a good idea if you want it to look decent.

Make up a router-like base for the unit and clamp guide rails to limit side-to-side motion. It takes very little to make such a base, which can be as simple as a bored out block with a slit and clamping bolt mounted to a piece of aluminum angle. One of my 1/4" air die grinders came with a convenient cylindrical section near the collet and if you go electric I think the Proxxon die grinders all have such a feature. I know the ones that take a 1/8"max. shank have a 20mm section and Proxxon sells various mounts to suit.

PS: I'd bet even something like the Bosch Colt trim router would do a pretty good job with 1/4" shank burrs for occasional use. I own one and while I haven't tried it on metal I'd bet it would work.

Yeah. The worst - when you need to stick a carbide burr into a bore with not much clearance, and the burr catches, and bounces around in the bore. If it is a 6" carbide burr, that can bend or break, all the worse.

For those and many other situations, I prefer electric die grinders with router speed controls. A friend who ports cylinder heads introduced me to it 25 years ago and it was a game changer.

It allows low rpm, excellent torque, and great feel. I can really bear down against the burr and workpiece. That creates stability and cutter support that I can't get with just my hands. I can feel the cutter tracing along the radius I am cutting, and I can feel the texture of the finish. Nevermind that carbide wants to be run fast - it works just fine at low rpm.

The lower speed is also crtical for abrasives - flap rolls, tootsie rolls, etc.

High RPM burrs have their place, but it is a very different technique.

Scottl- those trim routers should work just fine with a small-enough bit.

Stefan G even used one as the base for a edge chamfering tool. So clearly enough umph for the task. I've got the guts of a rotozip set-aside as a next project just for that purpose.

Why is it....Everytime I pick up the die grinder, I think I'm getting ready to doo dentistry on Shamu...Open wide please....

The instructions for my Metabo die grinder specifically say not to use a pear-shaped burr. The reason is that it can grab and kick the tool back towards you, making a mess, breaking the burr, and engaging the emergency stop function of the grinder. I've found the same thing happens with straight burrs if the burr is even close to the size of the hole that I'm enlarging.

I stumbled onto a solution! I've started using Inverted Cone Burrs. If it grabs, it pulls the grinder into the work. This releases the burr, it doesn't move around damaging the part, and it doesn't engage the emergency stop.

I just bought some more this month: RICO #312N 5/16" x 1/2" Inverted Cone Shape High Speed Steel Burr with 1/4" shank

Back when I could see good....I would simply concentrate on ONE spot of the hole at a time, taking care not to let the burr go anywhere else. Sort of like working around a clock. I think the tendency is to 'look ahead' at where you plan to go next and that's where the problems come in. Looking ahead os good for blending and general stock removal but when the burr is in a round hole that is close in size....it allows the pinball effect.

It is about technique and everybody has one. For most work I always had the forward hand firmly grasping the grinder, mindful of where the exhaust jets were if it's pneumatic. The forward hand, palm up, plant the knuckles (back of hand) firmly on the work as an anchor/shock absorber/pivot. The back hand controls the trigger AND the back end of the grinder. Gloves on the forward hand are important to avoid the shower of "needles" and absorb some of the vibration that will transfer into the work. Using the forward hand as a pivot I would use the rear hand to sweep across the area parallel to the surface like I was a horizontal mill. Just pressing the burr/wheel into the work at one place creates a radius and that always seemed to snag the cutter or generate too much heat. I always tried to keep the cutter/burr/wheel moving to create flat surfaces that could be disengaged from at any point if something didn't feel right, always cutting/grinding conventional. If it was a long bead of weld I'd just re-position my forward hand/anchor in a series of horizontal cuts. It may seem to take longer this way but firm control avoids the burr snagging/jumping and chipping a good carbide burr. For me, climb cutting/grinding had to be very light finishing passes or it would leave marks on the surface. Polishing with felt bobs was done much the same way. Hope this helped someone, other techniques are equally valid. Everybody has a different comfort level. This is what I do for flat work or blending. For holes or internal profiles I tend to do what GregSY posted above. No one technique covers all situations and you have to adapt to the task at hand.

I use the die grinder to put grease groves on the interior of brass sleeves, these are a few things I have to know the hard way.
A) Make sure you are in a very comfortable position avoid the death grip on the die grinder
B) Run a few dry passes
C) Find a place to rest your hands while making the pass(s)
D) Single versus double cut burrs, I don't know I have a few people about difference/application and received a couple very different answers.
E) If you require a nearly or prefect grove choose different method.
As far as chatter and jumping out of cut, start with light passes, and once you get the feel for how the burr is cutting in your particular material you can gradually increase the pressure on the burr only to a point. Pressing to hard will always lead to problems i.e. jumping the groove and chatter.
This only my experience and would like to hear some pearls of wisdom from others.

Hope this helps, and an excellent question.

IME smaller dia burrs are easier to control - I think? (as in I could be wrong) due to the smaller contact area that comes with a smaller diameter.

Another trick is don't try to take it all out at once - breaking a (say) 0.030'' cut in to 3 and using a wiping motion makes all the difference.