Rear parting off tool

I have been thinking of making a rear parting off tool holder and have looked a several ideas and kits available. I then spotted a photo in the book amateur lathe by L H Sparey page 201. He used a angle plate with two clamps holding the parting tool, as stated its for cutting screws to size. Has anyone tried this easy option on something a bit thicker, or have some other ideas. The reason for the question is that finding a lump of steel of that size and milling slots to accomadate a parting tool holder on a small mill, I would rather just buy one, if available.

I modified a toolholder off a ( i believe ) capstan lathe so maybe a hunt around on ebay will yeild something of use .

My original holder was some 50 x50 sq tube welded to a base plate and an old four position tool holder of my lathe welded to the top of the tube , worked well but looked ugly and was a pia to remove .

I made a rear toolpost for parting off using a piece of bar and some steel from my box of scrap. I can adjust the height of the toolholder and I have placed the toolpost at the rear of the cross slide and leave it there. I remove the toolholder though, when not parting off. It was well worth the effort.

Thor

I like the toolpost that Thor has made and looks not to difficult to do. A question about these toolposts that have the parting tool set at a angle approx. 4%, they say that they are adjustable, but the adjustment to centre is set by moving the parting tool, so that means you have no adjustment for what dia you need to part off.Thor's toolpost has the 4%, and the adjustment for height is on the post which can be locked with the bolt . Why is the parting blade at a 4% angle on these toolposts, what advantage is 4% to horizontal.

BOB BLACKSHAW:

You could consider the Hemingway kit based on the GHT design. The latter incorporated two p/o blades set at 7 degrees in an indexable turret; the smaller is used for up to c. 1.25" and the larger for up to c. 1.75". The blades are 1/16" and 3/32" thick respectively.

I agree that there may be times when the ability to adjust for diameter is useful but in practice the two-blade design works well. The effect of the 4 or 7 degree angle is to avoid the need to grind top rake on the tool which only has to be sharpened on the front face.

I'm sorry for these beginner's questions, but if I'm parting off brass then these 4 to 7% parting holders cant be used as I thought negative top rake for brass.

Hi Bob
I made one for my S7 it works fine here it s in action

Edited By Nobby on 14/12/2017 11:24:11

BOB BLACKSHAW:

I can't claim to be a beginner but I am certainly no expert; it's your own experience that matters.

GHT's Mk1 device dealt with your point by having one of his blades set horizontal but he later found this unnecessary for brass (as I do). The beauty of his rear toolpost is that any number of turrets can be made and quickly exchanged so that you could have zero or negative rake if you wanted. I used to use the KIT-Q-CUT blade and insert in a dedicated turret until the blade failed when I happily reverted to the standard turret with two HSS blades.

Hi Bob,

The reason for the 4 deg. angle on the rear toolholder is to get some rake angle. I mainly use the rear toolpost for parting off steel, and this way I don't have to grind the top of the HSS blade, just the front.
For parting off brass/gunmetal I use a "normal" parting off (with no back rake) toolholder mounted in my simple QCTP.

Thor

Hi Bob,

**LINK** I bought one of these and attached it to a holder I made from a piece of 75mm “ [ “ section channel. Just cut off one of the webs and drilled it to accept clamping bolts. Tried to send pictures but no luck here. If you send me your E-mail address I’ll send them.

Malc.

Many years ago, made a back toolpost for my ML7, and used the parting Tool inverted.

Sufficiently impressed that when I changed to a larger lathe, I made a four way indexing rear toolpost. This allows me to Front or Back Chamfer, as well as parting off. Being idle, and a bit of a hammer and chisel merchant, none of the tools have any top rake. All are used on whatever material is in the chuck at the time.

The parting blade came with the ML7, at least twenty years ago, (Been on the "new" lathe for fourteen years) and is still not worn out, (I fear the day when it is, for finding a replacement blade!).

Definitely +1 for a back toolpost, if only for parting off.

Howard

Sorry to resurrect this post . Finally made the prototype rear tool post for my lathe. Warco wm240. To make life easier there is no top rake to the tool, just clean up front face on grinder and the tool holder/ tool post is set for centre height so no adjustment. Works suspiciously well. It has transformed the parting operation so a worthwhile addition. Cost very little to make 1 1/4 sq and 2 1/4 x 1 inch, homemade T nut bit of studding and two bolts. Finished one will be painted yellow for visibility and to avoid parting off the chuck.

Gordon