Part 12- R-8 Tool Holder




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1. R-8 Tool Holder




·         Hold a round object up to 1” in diameter and 4 3/4” in length (length may vary depending on the piece).

·         Object to be ground may be tilted in proximity to the grinding wheel most any direction and rotated 360°.

·         Holder can be locked to not rotate, set to rotate (swing) 180° or unlocked with no rotational restriction.

·         Using the 360° Zero Set Dial, the holder can be locked in 15° increments.

·         A ½” collet, holds the drill sharpening fixture.


Basic Operation:

(there is a complete parts list at the bottom of this article)








The R-8 Collet Tool may be removed from the Index Head by loosening the Barrel Nut

Coarse Adjustment Lock Screw (Barrel Nut) and the Gib Lock to slide the tool holder

out from the back. You may have to back off the gib screws.





The Calibration Aperture had two functions.

It holds the end mill calibration tool and positions

the Stabilizing Bar for the  Drill Grinding Tool.


I put the tool on the surface plate with 1-2-3 Blocks to check the

R-8 Sleeve for run out. I found the sleeve to be very nicely ground

and at most .0002" of run out. This is well within the tolerance

for the Home Shop Machinist. (note: the Deckel grinder does not have

ball bearings). Any attempt to take the R-8 Sleeve bearings apart

will very likely result in catastrophic results.


Let me begin with this tool will work with no modifications.

I think that checking and repairing the Dovetail (see Part 10)

is important however, it will work “as is”.


The changes I made over time are improvements I made to make

the tool better for my use and suggestions for my readers. 

Many experimental changes I made are not included primarily because

they did not work or did not help improve the tool.



The following are the optional repairs I made to the R-8

Tool Holder to improve the usability, accurate use

and looks of the tool. You will see in my pictures

that #001 (how the tool appeared in its original form)

is not the same as the pictures that follow due to

changes I made.


Collet Alignment Witness Mark:

Looking down the cylinder of the of the R-8 Sleeve, locate the collet indexing nub

(photo #007). This is the protrusion inside the sleeve that the slot of the R-8 Collet

slides into. this nub and slot system prevents the collet from rotation in the sleeve.


Lock the sleeve so that the nub is located in the 12:00 position with the three-position

rotation lever (see photo #002 & #007).


Drill a shallow hole (witness mark) on the Sleeve Collar and the top of the casting.

I filled my marks with yellow paint for easy identification (see photo #007). This allows

easy location of the nub for installing the collets and can be used later for special tool setups.



Taking Apart the R-8 Dividing Head (Parts list photo # 999):


Make sure the 3 position lever is in the up locked position.

Remove the R8 holder from the Index Head.

Remove the Collet Draw Knob and any collet.

# 007a-Unscrew the Rotation Knob / 360° Ring Adjustment (RH Thread).

# 007b-The 360° Zero-Set Index Ring will slide off.

# 007c-Remove the two Tail Jam Nuts.  Loosen the outside nut first by lightly tapping it with a screwdriver.

# 007d-The Indexing Plate will slide off.

# 007e-Remove the two Thrust Plate screws to remove the plate.

Remove the Fine Feed Roller and Coarse Adjustment Barrel Nut (parts 12 & 13).

# 007f-To remove the Indexing Plate Spacer remove the square Key-way and the Spacer will slide off.






Index Plate:

My Index Ring was rubbing as I rotated tool. To locate the problem I

measured the Ring then the dial Index Plate. I found that the plate

had .010” of run out on the face. I chucked it up in the lathe using an

R-8 Tool holder in the chuck and turned it concentric to the outside diameter.

(see photo # 008 & 009).



STOP GROOVES in the Index Plate:

The grooves on the back of the Divider Plate are spaced to allow the user to subdivide the rotating tool into 15° segments.

There are two exceptions to this. If the yellow R-8 aligning marks are in the bottom position (photo # 007), the missing stops

are at 105° and 255°, these are the locations of the 180° Bumper Stops (photo # 999).


You can correct this by removing the Divider Plate and mark the groove that is the center of the two rotation stops.



Center the plate on the rotary table with the groves down.

Loosen and turn the plate over, groves up. Find an end mill that is close to the same shape as the groves.

Loosen the part just enough to be able to move it and using only the “X” axis and the loosened part to

zero on any of the stop groves using the “V” end mill.

 (warning: if you move the “Y” Axis the part will no longer be on center)


Adjust the Rotary table to the yellow mark that indicates the center groove between the two 180° stops (it is 7 notches to each stop). Tighten the part and recheck the fit of the end mill to the groove. With the end mill set between the 180° stops, zero the rotary table. Mill “V” slots in the top of the two Bumpers at 105° and 255°.


I went about halfway, .080” deep.

(see picture of digital microscope)




Thrust Bolt Adjustment Roller:

The Barrel Nut Coarse Adjustment Lock Screw (Barrel Nut) (see photo # 016) slides in and out for coarse adjustment. The Thrust Bolt Roller is the fine adjustment for the “X” Axis (in/out) Dovetail Slide.





I could not easily move the Top Slide Thrust Bolt Adjustment Roller with my fingers. The original part had parallel lines on the perimeter to provide a grip for the Roller. This did not work for me so I placed the bolt in the lathe to put a coarse knurl on the knob. Additionally, the roller wheel rubbed on the edge of the Dovetail. I machined off .030” of the Dovetail to make clearance for the wheel. This will not harm the effectiveness of the dovetail.



Next I made a new Thrust Bolt from scratch. This one has a larger wheel with holes around the perimeter to allow

insertion of a “Johnson Bar” (same as the Sherline Chuck uses) to rotate the bolt.


To allow clearance for the new roller I had to machine off more of the R-8 Body.


I have now made several Thrust Bolt Adjustment Rollers but am not yet satisfied with the results. (More to come later as I work on this problem).


Thrust Bolt Retaining Plate:


I tried to save the old Plate but the part is too poorly made to have a good working and nice looking finished piece.



 # 019-a


Make a new Plate. If the holes for the original Thrust Plate Screws are accurate, use Super Glue (Cyanoacrylate) to hold the old plate to the new material.


 # 19b


Use the old part to draw the shape on the new material. I used a sharpie to get a nice fat line that is easy to see. On my Plate the hole for the Thrust Bold was not accurate so I had to add material to the drawing for my new Plate.


In the milling machine, line up, drill and tap the for the two Thrust Plate Screws that hold the plate to the tool. Use #30 (.128”) for the MM 4-.7 thread.


# 19c




Screw the pieces together to insure the will not move during the machining.


If the old Thrust Plate Center Hole is accurate to your satisfaction, zero the old hole and drill the center in steps as big as you have drills then finish with the boring head.




























 # 19d


Using the rotary table cut out the outside circle (don’t cut off the Thrust Bolt tab!!!!).





The parameter is completed on the rotary table.




















# 19f




Complete the tab.





















# 019g



Old and new Thrust Bearing.


# 019h



360° Index Ring Spacer (part #2):


There was .057” gap between the 360° Index Ring and the Thrust Plate. This will allow easy access for dust to get into the Ring Bearing. I was able to pull out the keyway and slide off the spacer.



Square up and lightly clamp the spacer in the lathe. I took off .030” to carefully close the gap. I took off small amounts (.005”) material until I was satisfied with the results.





R-8 Tool Holder Parts List:


1-  R-8 Dividing Head Body

2-  360° Index Ring Spacer

3a-Thrust Plate Screws

3b-Thrust Bolt Retaining Plate

4-  Index Plate

5-  Jam Nuts (X2)

6-  360° Zero Adjustable Ring

7-  Rotation Knob / 360° Ring Adjustment

8-  R-8 Collet Draw Knob

9-  3 Position Lever Spring

10-3 Position Plunger

11-Plunger Handle

12-Coarse Adjustment Barrel Nut

13-Thrust Bolt Adjustment Roller






Terminology of parts Disclaimer:

Several names of the parts have been taken from the Deckel Catalog; to insure you the reader, will always know what part I am referring to. I have applied the identification of parts from other machines, catalogs and some I created for a clear description of the parts function, (eg. Top Slide Tool Holder).