Lathe solid tool post mount thoughts

[SouthernChap]

I love it!!

My lapping plate is an old Lee Valley surface plate 9" X 12", sourced from offshore. It isn't very accurate and very small. I paid about 29$ for it, but didn't realize it was useless for machining. It is perfect for a single sheet of wet and dry.

I've used float glass for lapping as well..

I assume that's what the lapping plate I have is, float glass.

 

[dabear3428]

Seems like a solid plinth would be an opportunity to build in a 29.5* position. Several QCTPs have dowel pin holes for positioning - so add another. If it doesn't exist, create it. Accept nothing that is nearly right, nor good enough. With apologies to H. Royce...

GsT

the angle of the QCTP is not the issue it is the travel angle of the compound slide.

 

[GeneT45]

the angle of the QCTP is not the issue it is the travel angle of the compound slide.

Doh! I'm a dunce...

GsT

 

[dabear3428]

I've contemplated eschewing the swivel 2-bolt mount in favor of a 4-bolt mount directly to the cross-slide. The video shows the 4-bolt direct mount is at the edges of the cross-slide, and into the dovetails. In may case, drilling and tapping the dovetail areas would constrain bolt diameter, probably to M4, while doing the same outside the dovetails constrains bolt length to 5mm or so, and would probably require custom facing/parting the bolts so they don't protrude past the bottom of the cross-slide.

My instinct tells me bolting through the dovetail area is the better choice, I can always add another bolt making it a 6-bolt mount if needed.

View attachment 488593

that is what i did.
the added benefit is that the large plate bolted thru the dove tails improves the rigidity of the cross slide as well.
also i machined 2 bolt holes so that i could move the QCTP back for more swing if needed.

 

[RaisedByWolves]

Doh! I'm a dunce...

GsT

Well, at least you have that worked out.

There is some magic trick to having a few precise dowel locations in regards to the multifix style, hence the name, but I disremember all but putting your threading tool perpendicular to the work quickly.

Something like with two or three pins you have the ability to change the angle of the tool holder in 1* increments.

 

[dml66]

I made some progress on the solid QCTP mount.

I found that I really need to include a 3/32" shim riser for some cutting tools, mostly small diameter boring bars. The main 1.5" thick riser block is not quite enough to get a boring bar cutting point just above the spindle axis, or even dead on it. For most turning operations though, the riser block is tall enough.

Here's the cross-slide showing the four M4-0.7 thru-tapped holes in the dovetails:



Here's the block and shim temporarily installed, the block is mounted above the shim:



I drilled and blind tapped 3 M10-1.0 holes for the QCTP stud, the one furthest in from the cutting tool edges offers the most rigid position for the tool post but that may cause the block to contact the chuck before the cutter is where it needs to be on the part. The two other holes give up some rigidity but ensure that the cutter leads the mounting block into the work.

Here's the final assembly, including the QCTP with a boring bar:




I'm in a quandary as far as achieving a super flat and smooth finish on the shim riser and mounting block; I spent a couple hours going at it with sandpaper on a float glass plate, just not seeing any serious progress. A friend works at a local automotive machine shop, he might be able to run the riser block through a head grinding machine for me, but the shim riser may be too short for the machine.

I'd also like to add a jam of some sort to prevent the QCTP from swiveling, even though I've never see it actually do that.

Once I get the new screws it'll be time to make some chips .

 

[GeneT45]

Does your QCTP have a/some hole(s) on the bottom where you could insert a dowel pin to prevent rotation? Could you add one?

I can't tell if it's the photo or not, but it looks like you're giving up some swing since the plinth is substantially larger than your toolpost.

GsT

 

[dml66]

Does your QCTP have a/some hole(s) on the bottom where you could insert a dowel pin to prevent rotation? Could you add one?

I can't tell if it's the photo or not, but it looks like you're giving up some swing since the plinth is substantially larger than your toolpost.

GsT

The QCTP is mounted in the rightmost stud hole where yes, it will give up some swing. By mounting it in the leftmost stud hole, the QCTP is flush with the edge of the mount, no swing is lost.

I don't know if the QCTP has a hole for an indexing pin, I'll take a look. I was thinking of using a 2" or so long piece of 3/8"x3/8" square bar stock screwed into the mount base, it would have two grub screws facing the QCTP which would be snugged up against it thereby preventing it from swiveling. I may have seen an arrangement like that on this site.