Die grinder or dremel - relieving cast iron

I need to remove a couple of millimeters of material from the floor of this cutout (the ledges at either end) in the knee of my Harrison mill. I'm replacing the lead screw and bronze nut with a ball screw and I've not quite go enough room. Would i get by with a Dremel for fourty quid or am I best of with a die grinder (a cheapish one, no more than a hundred quid). The surface is as hard as nails. I tried to scrape it with the end of a file as it didn't even scratch it. I assume it has sand in it as it is 'as cast'. The ribs/floor is about 8mm thick and most of the material that I'll remove is in the center to allow the underside of the cylindrical ball nut carrier to clear. The trough/cutout is about 40mm wide/35mm deep, 220mm long to give you an idea of size.

It could be done with either. A die grinder may be cheaper with the cost of the number of burrs needed being lower. Removing 2mm over that area may get a little time consuming with the smaller burr available for the Dremel. It is also a question of wether you can re-use the tool later.

Not a real Dremel but I tried my LiDL version on a similar job both with grindstone and flap wheel. Asking rather too much of it I thought. Needed to be awful careful with a grindstone as it wanted to bounce off and attack the wrong places. Probably because the tool is so light.

I didn't actually try my air die grinder. Although its heavier and more stable than the LiDL "Dremel" its stiil a bit bouncy-offy in my hands. Probably because I don't use it enough (about 5 or 10 times in 20 years) to get the muscles and reflexes dialed in. As I recall it I found an angle grinder as challenging the first half a dozen times but 40 years on I'm perhaps a little too casual.

What I found to work well was a small rubber sanding drum on a shaft held in a battery drill chuck, Cheap Machine Mart set got perhaps 40 years ago 'cos it looked useful and sat on the shelf ever since. Killed all the sanding cylinders in the right size but got the job done. This one **LINK** looks the same. I imagine the resilience of the rubber drum helps keep it under control. But you won't be able to get things dead flat.

A band filer might work well too. I have a LiDL one that is effective in the right places but it positively eats abrasive bands.

Clive

Have a look at the Chinese Foredom flexible shaft grinders on ebay. I bought one to do some cylinder head work some time back and I've used it for all sorts of things since. Get one which will take a 6mm shank burr. Garyson burrs are very good but you may need a diamond burr to get through the skin.

Just ordered an evolution die grinder. C grade (refurbished stock) direct from evolution, £40 with free postage. . Downside is that it is 110v so I'll need to hire a transformer but luckily our local tool hire shop has just reopened today.

Now to find some burrs, the Garryson ones arent that easy to find on line, at least not at prices I can afford.

Edited By Mark Davison 1 on 11/05/2020 05:49:19

Just an idea - anyone tried a wood router and small carbide cutter for this sort of work ??

Or modify the ball nut carrier to clear????

You can get a cheap die grinder on ebay for much less than your price, and it is ten times as powerful as a Dremel. They will hold carbide rotary burrs up to 3/4" diameter. If you have a compressor, a pneumatic die grinder is even cheaper than an electric one.

The pneumatic one will really eat metal with the carbide burr but be sure to be wearing eye protection and leather gloves as the metal particle as tiny an very sharp. If you get one in your finger it is nearly impossible to see it to be able to remove.

Use a die grinder with a HSS burr. I have both a dremel and an compressed air die grinder. I had to remove some iron on the cast iron on the counter shaft support of a 1958 mk2 S7 to allow a link belt to be used. You can pick up cheap burrs online with either 6mm or 1/4" shank to suit your die grinder.

Peter

In the end Evolution cancelled my order as they didn't actually have any. They sent me a 20% off code as an apology so I went and bought a new one with 4 carbide burrs , some flapper wheels and cut off disks for £52. Still 110v but I can live with that.

I used a mounted point to get through the skin rather than risk wrecking a new burr. In hindsight I think that was overly cautious. I then switched to the burr and it does remove material quite quickly and under control.

I've taken more off since I took this photo (theres plenty left) and tidied up the shape a bit. I now have (just) enough depth. Oily rag - the mounting block is as slim as I can make it already.

Edited By Mark Davison 1 on 14/05/2020 19:42:40

Edited By Mark Davison 1 on 14/05/2020 19:44:23

I have a Dremel in addition to pneumatic and electric die grinders with 1/4" collets. I would never consider a Dremel or similar tool for that much metal remover. Now that I have a compressor capable of driving the air tool it would my first choice. The electric die grinders are suitable to the job but are heavier and less comfortable to use.