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View Full Version : Grinding - "Snagging" versus "Off Hand" (toolingu homework)



PStechPaul
09-25-2014, 01:12 AM
I just finished a set of lessons on www.toolingu.com for my machining class, and one lesson concerned the difference between "snagging" and "off hand grinding". Here are some test questions regarding this:

Snagging vs off-hand grinding

Offhand grinding, workpiece held in operator's hand (T) So this must not be done for snagging
Offhand grinding removes excess material without regard to surface finish (F) This applies to both operations
Snagging is used for large amounts of material removal (T) Apparently this does not apply to offhand grinding
A coated abrasive belt may be used for snagging (F) So an abrasive belt is only for offhand grinding

I have never before heard of snagging, except as something that might happen to a piece of clothing on a sharp object like a lathe chuck or end mill, or an illegal method of fishing. Apparently the educators who developed this instruction felt it was important to know the difference between these terms, as it was on the final exam and other exercises. But an internet search does not come up with much on "snagging", except in the toolingu material, and a few "snagging wheels" and a "snagmaster", which appears to be a large floor mounted grinder with a tool rest apparently for offhand grinding:

http://www.uselectricaltool.com/snag76.html (snagmaster)
http://www.toolingu.com/definition-250120-3496-snagging.html
http://www.pacificindustries.net/portable-snagging-wheels-337599.html

So is this something important to know, or is it "academic"? After two online classes on grinding, it has not described just how one should perform these operations on a standard pedestal grinder.

Just for fun:

http://en.wikipedia.org/wiki/Snagging (fishing)


https://www.youtube.com/watch?v=2TQAupcJVgw

jhe.1973
09-25-2014, 02:32 AM
Hi Paul,

Guess what, I'm still alive!:D

I think I remember hearing the snagging term used in foundry work where the various extra metal (sprue and flash, as examples) are ground off castings.

Perhaps the writer of the course material is referring to this when the casting is held in a vise and the material is removed with a handheld grinder.

J Tiers
09-25-2014, 08:35 AM
"Snagging" is generally a rough "cleanup" grinding done to big castings and maybe fabricated pieces. Usually a large industrial version of an angle grinder, or something similar, is used.

"Offhand grinding" is where no fixture is used, such as grinding a toolbit freehand, vs using fixtures to set the angles..

TGTool
09-25-2014, 10:05 AM
In my experience and training the terms were used interchangeably to mean hand guided grinding as distinct from machine controlled. A pedestal grinder would often be referred to as a snag grinder. I presume the term came from foundry use and I have seen a video of a huge grinder used on castings where the operator controlled a suspended grinder and could move it around as required. I've never seen such a tight distinction made between offhand and snag grinding and IMO someone is really putting too fine a point on it.

Weston Bye
09-25-2014, 11:25 AM
To further confuse the issue, in my local experience an angle head grinder was often referred to as a snag grinder and was used in welding fab to clean up a flame cut edge or smooth a welded area to remove wayward metal beads, boogers and berries.

Offhand grinding was done at the pedestal grinder, holding the workpiece in ones hands.

EVguru
09-25-2014, 01:16 PM
I think I remember hearing the snagging term used in foundry work where the various extra metal (sprue and flash, as examples) are ground off castings.

I've always know that as fettling in the UK.

jhe.1973
09-25-2014, 01:44 PM
.................. I've never seen such a tight distinction made between offhand and snag grinding and IMO someone is really putting too fine a point on it.

Hi Everyone,

I feel the same way!

This is perhaps an example of the saying, “Those that can, do. Those that can’t, teach”

I feel that most of the contributors to this forum belong in the first group above.

;)