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Boucher
10-06-2012, 10:34 AM
This post presents a rear mounted parting tool that has several good design features.
http://www.machinistblog.com/rear-mounted-parting-tool-holder-for-sherline-lathe/
The front – rear-parting discussion/argument does not need to be revisited here. The significant points are that this tool accurately positions the cutter perpendicular and on center.

This is my implementation of this concept adapted to my Nardini Lathe.
http://i109.photobucket.com/albums/n50/boucherbyron/NewToolPost.jpg

Here is how it looks mounted on the lathe.
http://i109.photobucket.com/albums/n50/boucherbyron/RearPartingPost.jpg

ikdor
10-06-2012, 01:27 PM
I like it a lot, makes me want to have a mill :-)
Did you machine the end of the screws on top to prevent them from pushing the blade to the side when tightening? Or is that a non issue?

Igor

flylo
10-06-2012, 02:14 PM
Nice job & great idea! Thanks

philbur
10-06-2012, 02:19 PM
What top rake angle do you use?

Phil:)

Boucher
10-06-2012, 03:08 PM
I like it a lot, makes me want to have a mill :-)
Did you machine the end of the screws on top to prevent them from pushing the blade to the side when tightening? Or is that a non issue?

Igor

The first screw that was tried is shown on the right in this photo.
http://i109.photobucket.com/albums/n50/boucherbyron/IMG_0069.jpg
This is made by drilling the end of the screw and inserting a short piece of copper wire that is swaged in place. When this screw was tightened it turned a burr on the copper. Several alternatives were considered. The threaded hole is deep enough that a 3/8” slug of brass was used in contact with the blade and the screw tightened over that. The clamping feature of Mikey’s design would eliminate these problems but it would have been harder for me to implement.

Boucher
10-06-2012, 03:20 PM
What top rake angle do you use?

Phil:)

Phil, There is no top rake. In order to be on center the blade is horizontal. This is a P-5 Parallel T shaped blade. I sometimes use the Dremel tool to grind a center groove to help fold the chips for better side relief in the slot.

J. R. Williams
10-06-2012, 11:57 PM
I use an insert cut off tool that is rear mounted and run the lathe in reverse for cutting off.

Boucher
10-08-2012, 05:35 PM
Well most of the day has been spent tweaking the upside down parting tool in the rear tool post. Most of this was fixing little mistakes like the mounting bolts were bottoming before establishing a good clamping force. Evaluation started with some 1 1/4 Stressproof which is easily machined. Chatter raised its ugly head and I have done everything from honing the blade to adjusting the gibs. The material is being held in the 6-Jaw and doesn’t quite extend through the headstock. I am suspicious that the chuck may be bell mouthed or the unsupported end of the stock may be aggravating the problem. Will report what I find tomorrow.

DR
10-08-2012, 09:43 PM
Phil, There is no top rake. In order to be on center the blade is horizontal. This is a P-5 Parallel T shaped blade. I sometimes use the Dremel tool to grind a center groove to help fold the chips for better side relief in the slot.

My guess is the chatter you mention is due to the zero rake.

I have a couple holders made for that cut off blade, they all have built in rake.

With a raked solid non-height-adjustable holder the blade is only on center at a certain extension out from the holder. You have to plan accordingly and settle for an extension that works for the majority of cut offs you'll be doing.

cameron
10-08-2012, 11:08 PM
The holder may not have the rigidity needed for good parting off, hence the chatter.

J Harp
10-09-2012, 06:51 AM
I suggest milling a pocket for the mounting bolts, rather than milling a channel all the way across the holder. Leave as much front and back wall thickness as possible while allowing the holder to be bolted down solidly.

PixMan
10-09-2012, 07:42 AM
Your machine is certainly stout enough for this to work. I believe you'll be fine if you make two alterations. One, move away from HSS blades and get into a good carbide insert parting tool. You'll never look back. Secondly, a better way to clamp the blade might be to imitate the Dorian holders. I find these to be among the most chatter-free type of block available. If you could get your clamp system similar and hold more of the blade, I believe that would further reduce chatter.

http://img.photobucket.com/albums/v466/kenm10759/Dads%20shop/photobucket-7668-1315256060736.jpg
http://img.photobucket.com/albums/v466/kenm10759/Dads%20shop/photobucket-3090-1315255798147.jpg