Tool Arm, KMG vs DD Extreme?

M

matthewhoffman

Joined
Nov 19, 2016
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Hoping to get some opinions before I shell out some (serious) money for one of these tool rests. I'm planning to try my hand at scandi grinding, and one of these tool rests seems like a more practical/versatile idea than cobbling together jigs. I have the older, "classic" style KMG. The DD Extreme seems like a nice piece, but expensive! I'm wondering if it's a better choice than the tool arm that's now being offered by Beaumont. Thoughts?

- matthew
 
i own the DD rest. its ok but has a slight movement or wiggle if you press too hard on it while grinding. the kmg looks nice, but i have no experience with it.
 
John, thanks for the insight. I read in older threads that the DD had some play, but I assumed it had probably be corrected. Apparently not ...

I've also wondered about the Northridge RAT arm. Don't know if it's plug and play with the older KMG.
 
I was just ogling the new KMG tool rest myself. Simple adapter lets it work with the classic KMG, which is nice.
However, I saw some clever stuff at Blade, and decided that with a cheap electronic angle finder and a simple square holding jig, I could tilt the platen repeatably for that kind of grinding and get most of the way there for $20 and some scrap steel. Just finished the holding jig yesterday, haven't tried it yet. Slower to mess with? Yes, but also many fewer degrees of freedom to worry about. (yeah, I still want the fancy tool rest, but ~$300 and out of stock)
 
I have both and in all honesty each has a fair share of pros and cons. As john april john april mentioned the DD rest does have a bit of give when applying pressure. Most times this isn't a huge deal but there have been several times where my grinds were slightly off due to the flex in the table when grinding. Also, manipulating the tables height and angle is MUCH more time consuming than the Beaumont rest. However, in my opinion where this attachment really excels is when you need to grind at extremely steep angles. The ability to come right up to the platen at a very sharp angle is something I have never seen by any other tool rest. I had Don build me a custom size XL table for mine and the extra real estate is very nice imo.
In contrast, the Beaumont rest is much quicker to change angles, sturdier, and (with exceptions) offers greater versatility. Unlike the DD rest I have not found the Beaumont to be easy to manipulate for use at steep angles without leaving an enormous gap between the platen and table. Also, this is personal preference but imo the work table is woefully small. My final gripe is with the compression knuckles. When tightening them there is a tendency for the table to cant in one direction or another depending on the knuckle used for final adjustment. This is also true for the work rest on my Beaumont disc grinder table and appears to be a side effect of the locking mechanism. Easily overcome but slightly annoying when chasing square or pre determined angles.
While it may appear I am being overly critical it should be noted that I love both rests and would have a hard times picking one over the other. Not knowing exactly how you plan to use your tool rest I believe you will be both happy and possibly frustrated with whichever you choose, but will learn to overcome the shortcomings for either one.

Blessings,
Joshua
 
Much thanks for the detailed impression. No such thing as "too critical." Your experiences are valuable. I'll be sleeping on this one!
 
that northridge RAT arm looks pretty cool and well built. for 400 clams i sure hope it does not give or wiggle . does anyone own one ?
 
According to George at Northridge (who responded quickly to my email), their RAT arm can be adapated to the older-style KMG. I've decided to sit tight until I have the $$ to buy one of their grinders ... which I wish I'd done in the first place! For KMG owners who are interested, here's George's comment:

We have a secondary arm clamp that bolts on to an existing arm, but the rat arms main arm would have to be cut down for clearance if your Interested I could try to find some pics and send them ?
 
What's the max angle on the dd extreme you can get in relation to the platen?
 
I have a tool arm that I don't use anymore and would sell. The RAT is great but I still can't believe that in 2019 the "best" tool arm out there can't provide linear Z motion without losing the rotational Z position. My arm has full independent 6-axis motion. I can stand on my tool rest without anything slipping. All offers considered.

Old pics of my tool arm, installed on a KMG clone. Note that the arm has to bolted to the underside of the grinder.

https://www.flickr.com/photos/110785734@N05/albums/72157659862547056
 
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