Can't tighten down my quick change tool post due to Grizzly's poor design

[Toolmaker51]

Stioc - If you find that the tool post still wants to rotate a bit, it may be because the area just around the mounting bolt is slightly domed. The cure for this is to chuck up the tool post, get out your old 4-way to hold the cutting tool, and cut a shallow relief (maybe .010") around the center hole and out to about ¼" away from the edge of the QCTP. This will place the friction (between the compound and the QCTP) at maximum radius.

View attachment 293720

Of all remedies, this is the most beneficial, a relief. Cutting a relief establishes a 'land'. Just as it sounds, that becomes solid mount.
The Grizzly design or tool post are compatible in theory, equivalent to any other lathe or post. The failure was execution of one, maybe both. Post less likely as it is ground. A particular relief depth is not the consideration, sufficient clearance is. Note entrance hole of bolt in compound, chamfer of thread not visible, and small chamfer in post. That alone MAY have been the issue. Tapping 'always' raises a burr. There also could be a wire edge remaining in post, where drill exited, not removed by small chamfer. Could keep post from sitting flat on compound.
There are so many fitments lacking relief cuts, which cost mere pennies during manufacture.
One more good reason to keep feeler gauges, Dykem and felt-tip pens handy. In 2 distinct colors........

It's time [again!] to define what some consider a mere hobby. BS! Anything done as a pastime, which is otherwise alike to industry, differs only as not for profit. In some countries that home shop IS the industry. Even profit not the best measure, we invest without hint of compensation, for what seems to benefit us alone.
When a country should collapse, who do you think will be up front getting it running? Those jokers sitting in cubicles?

 

[savarin]

I found a brown paper shim under my tool post worked a treat to stop twisting

 

[Toolmaker51]

2-1/2 explanations. I'll bet the paper was full size the toolpost.
The main change is certain, different friction characteristic compared with metal to metal.
A high spot compressed one area, and contact widen.
Like machining a relief, but the center was not high as remedy in answer to earlier post.

 

[Tozguy]

If the bottom of the QCTP is flat and the top of the compound is also, that is how you will get the greatest area of contact and traction. If the compound is not flat, rather than dish out the underside of the QCTP to accommodate the misshapen surface of the compound it is better to fix the problem surface on the compound.
Otherwise by 'relieving' the underside of the QCTP there will be a risk of further deforming the compound mounting surface in use. The QCTP body is by far the more rigid of the two parts and tightening the mounting bolt will only serve to deflect the compound into the 'relief' cut in the QCTP.

 

[jwmelvin]

Two flat surfaces are great when placed together but when clamped with a single bolt, the stress is focused around that bolt. A relief will move the stress outward and result in much better torsional resistance. It also has much better vertical stiffness. The joint with a relief is better in all ways.

 

[Tozguy]

Re: 9x20 tool post flex

• 
  Re: 9x20 tool post flex
  
  At last I've finished it.
  Took longer than I thought as I had to make a couple of fittings and decide upon the order of work but only two days once I started.
  The first job was single point threading the 14mm shaft then drilling and tapping the bottom end 6mm.
  I made a test chunk with a 14x1.25 tapped hole to test the thread and it felt very good. (photos are too blurry to upload)
  Next I made some clamps and bored the compound 12mm then used the tap to finish the thread.
  View attachment 90688
  
  Reassembled the compound with the new 14mm shaft and turned down a bolt head to make the spacer to (in my mind) strengthen the fitting.
  The drawing gives the dimensions
  View attachment 90687
  
  bolt, spacer, countersunk 6mm bolt, bottom of compound showing the recess left after removing the original shaft.
  I countersunk the spacer with a walmart special countersink that I thought had no chance of doing the job but I was pleasantly surprised.
  View attachment 90679
  
  The fixing from underneath, a tight fit and flat.
  View attachment 90689
  
  
  The whole unit is assembled with high strength lock tight so I hope I dont have to disassemble it in the close future.
  The first tryout was like chalk and cheese for flex compared with before so now its the turn of the donut then brass gibbs.
  I forgot to take a pic fully reassembled but we all know what it looks like.
  
  So much to do so little time.​

View attachment 90679 View attachment 90687 View attachment 90688 View attachment 90689

but ultimately the compound is the enemy. Makinging a solid platform for the qctp and only using the compound when needed is a better solution on a 9x20. That let me start taking much heavier cuts and part larger diameter steel more successfully.

 

[Toolmaker51]

Any threaded fastener 'X' is chosen for it's diameter, thread pitch, and material to deliver and retain administered torque. Torque is not tightness per se, but measurement translated from stretch; planned deformation of the fastener. Pulling a wrench is no guarantee of secure fitting.
Sought after stretch is affected by many factors; friction of threads and washer faces, bending stress when those faces are not parallel, temperature and thermal differential, condition of surfaces being clamped, sealing requirements [ie gaskets], area to be clamped and more.
Mechanical connections are subject to specific primary/ secondary forces by design. A pipe flange or carburetor mount is linear, a drive shaft or pump & motor is axial.
A tool post directs linear downforce into cutting depth [part of centerline importance] and lots into axial, as it directs into feed rate. The distance between tool tip and the post fastener multiply axial load for the post/ bolt/ face combination.

Simple visual demonstration or real test. Face off two plates of same size at same RPM and feedrate; then one drilled and tapped for a large screw, clearance hole the other but no chamfers.
Assemble finger tight but securely. Holding one in each hand, twist them in opposite directions.
Next, mark one with a few strokes of felt-tip and lap just a couple 45° strokes on flat dry abrasive. Observe that the center nearly guaranteed shows less tool & pen marks than perimeter, clearly a raised surface. The 45° strokes and pen illustrate evenness of surfaces.
Next relieve center of one about 1/2 it's diameter [surface area] and chamfer the parts as is common. Assemble the same as possible manner, and twist. It may still move, but greater effort required. That tiny but same amount of torque was distributed over lesser area = greater load per square inch.

Not to say QC tool posts need a relief, hardly any have them. But .010 or .015 corrected unknown condition of unsatisfactory compound/ toolpost connection. Without a surface grinder, that would be not easily fixed.