# Removal and Replacement of the Grizzly Mini-mill Spindle Head Gears



## HMF (Feb 9, 2011)

From: 
http://aspinock.com/7x10minilathe/Kinda-Old/MiniMill/grizzly mini-mill.htm

Removal and Replacement of the Grizzly Mini-mill Spindle Head Gears
Preface 
Spindle Assembly Removal 
Spindle Assembly Disassembly 
Gear Removal/Replacement 
Spindle Assembly Reassembly 
Spendle Assembly Replacement 
Footnotes 
Measurements 
Checklist 

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PREFACE 

The following set of instructions are intended as a guide. Your experience will differ. Consult the manufacturer's illustrated parts breakdown and parts list throughout this process. 

The part nomenclatures used here are as stated in the Instruction Manual. As such, they may not equate to common English terminology (e.g., "fuselage" vs. column body). 


SPINDLE ASSEMBLY REMOVAL (see diagram, page 11, of the Instruction Manual) 


Unplug the mill 
Remove the drawbar, washer, bushing, and all tooling 
Remove the speed control box, p/n 111 
Remove the outer plate (4 screws) 
Remove the 3 attaching screws inside 
Re-attach the outer plate, leaving the 3 attaching screws inside for safe keeping 
Remove the motor (4 screws) and motor seat, p/n 127 &amp; 130, as one assembly and set them on the mill bed 
Remove the upper end washer and screw, p/n 102 &amp; 103 
Using the adjusting handle, raise the spindle head as high as it will go, until the pinion gear, p/n 50, disengages from the gear rack, p/n 46 
Set the limit block, p/n 65, to hold the assembly in place 
Remove the connecting block, p/n 76 (2 screws) 
Loosen the gib (3 screws) and the handle, p/n 30 
Lift the spindle box and spindle box seat, p/n 49 &amp; 63, off the fuselage (caution: it's heavy). Ensure the gib, p/n 45, doesn't fall and break. 

SPINDLE ASSEMBLY DISASSEMBLY 


Remove the cover, p/n 96, over the fine-adjustment rod (2 screws) 
Remove the bracket, p/n 89 (2 screws) 
Detach the spindle box seat, p/n 63, from the spindle box, p/n 49, by unscrewing the 4 bolts (p/n 60) at the rear of the spindle seat (note: the diagram on page 11 labels the spindle box as p/n 49 - on page 12 it's incorrectly labelled as p/n 47) 

At this point, if only lubrication of the gears is desired, skip to Spindle Assembly Reassembly 

GEAR REMOVAL/REPLACEMENT (see diagram, pg. 12, of the Instruction Manual. You must remove the idler gear and shaft to replace the transmission gears) 


Idler Gear/Shaft Removal 
Remove the top gear, screw, washers, and key, p/n 132 &amp; 138 (the upper key is not shown in the diagram) 
In preparation for the next step, either elevate the bottom of the spindle box by putting blocks on each side of the idler shaft or lay the spindle box on its side 
Using a soft-faced hammer or other appropriate tool (see footnote #1) , tap the idler shaft, p/n 113, from the upper end (not the end with the snap ring, p/n 115) until it is free from the upper bearing, p/n 139. The shaft and lower bearing may come out of the spindle box as one. This is preferred. 
Slide the transmission gear, p/n 140, off the shaft as you remove the shaft/bearing from the housing. Remove the shift bar, p/n 141, from the linking board, p/n 142, during this process.  Leave the key, p/n 114, in the shaft. 
If further disassembly is required, set these parts aside, else proceed to Idler Gear/Shaft Replacement 
Transmission Gear/Spindle Removal 
Using a chisel or equivalent, mark the location of the spindle nut, p/n 119, on the spindle, p/n 79 (you'll need this reference point to tighten the nut back correctly) 
Loosen the set screw in the spindle nut (not shown in diagram) 
Engage the spindle nut with the sprocket wrench 
Using a separate wrench(see footnote #4), grab the bushing 
Remove the spindle nut, p/n 119, by rotating the nut CLOCKWISE (NOTE: it is a LEFT-HAND THREAD)(see footnote #5) 
Remove the spacing ring, p/n 118 
Remove the key, p/n 120 
Place the spindle box right-side up on two blocks, one on each side of the spindle (to allow the spindle and bearing to fall through during the next step) 
Using a soft-faced hammer or other appropriate tool(see footnote #1), tap the spindle from the top until it is loose from the upper bearing. The spindle and lower bearing may come out of the spindle box as one. This is preferred. 
Continue with the spindle removal until the spindle is removed. This will leave the transmission gear, p/n 80, and the top and bottom spacing rings, p/n 116, in the spindle box. Remove the gear (you might have to joggle the high/low gear shift, p/n 107/8/9, to get it out). Leave the key, p/n 78, in the spindle shaft (see footnote #3). 
Transmission Gear/Spindle Replacement 
Insert the new gear, p/n 80, in the spindle box 
Make sure the gear is properly oriented (large gear at top) 
Make sure there is one spacing ring at the top of the gear and one at the bottom 
Insert the spindle/bearing assembly back through the bottom hole of the spindle box, then through the lower spacing ring, p/n 116, the gear, p/n 80, the upper spacing ring, p/n 116, and into the upper bearing (see footnote #2) . Align the key in the spindle with the key slots in the gear and the bottom spacing ring during this process 
Place the spindle box upside down on two blocks, one on each side on the spindle 
Using a soft-faced hammer or other appropriate tool (see footnote #1) , tap the spindle from the bottom of the shaft until the keyway in the upper portion of the spindle shaft is fully exposed above the upper bearing 
Lay the spindle box on its side 
Insert the key, p/n 120, into the keyway 
Insert the spacing ring, p/n 118, over the spindle shaft 
Continue tapping the spindle from the bottom until the threaded portion is about 2 threads past the top of the spacing ring 
Turn the spindle box right-side up 
Using the same wrench setup as during removal, screw the spindle nut on COUNTER-CLOCKWISE until it is tight and the marks you made in instruction B.1 are aligned 
Tighten the set screw in the spindle nut 
Verify that everything moves freely 
Idler Gear/Shaft Replacement 
Insert the gear , p/n 140, and the shift bar, p/n 141, into the spindle box. Ensure the gear is correctly oriented (small gear at top), and that the shift bar is engaged around the gear and into the linking board, p/n 142 
Insert the idler shaft and bearing into the bottom of the spindle and through the gear(see footnote #2), engaging the key into the slot in the gear 
Using a soft hammer or appropriate tool(see footnote #1), tap the idler shaft/bearing assembly back into the upper bearing until the lower bearing is fully seated. If needed, tap the shaft back out from the top so that the snap ring, p/n 115, is not touching the bottom bearing 
Reattach the top gear, key, washers, and screw, p/n 132 &amp; 138 
Verify that everything moves freely (see footnote #6 ) 

SPINDLE ASSEMBLY REASSEMBLY 


Assemble in reverse order as disassembly. 

SPINDLE ASSEMBLY REPLACEMENT 


Place the spindle assembly on the fuselage, allowing it to rest on the limit block, p/n 65 
Insert the gib into place and adjust loosely 
Finish assembly in reverse order as disassembly 
Adjust gib and handle pressure as desired 

FOOTNOTES 


I used a hammer and block of wood for this process. An arbor or hydraulic press would work as well. Main concern is not damaging any of the metal parts 
This is a very tight fit. Be patient but firm in pressing the gear back on. Force it on using your hand, not a hammer, to protect the gear. I slightly filed down the edge of the slot in the gear and the top edge of the key to encourage their engagement. A little 3-in-1 oil helped, too 
This would be a good time to drill lubrication holes in the spindle box if so desired 
Channel locks should work 
You may find it easier to use the sprocket wrench on the bushing by inserting the nipple on the wrench into the hole in the side of the bushing, and a different wrench on the spindle nut 
Now would be a good time to lubricate all the gears, if desired 
.
MEASUREMENTS 
Gears Gear Total Height Larger Gear Smaller Gear Gear Height 
080 (Spindle gear) 1.75" 2.66" dia., 0.34" width, 29 teeth 2.01" dia., 0.35" width, 21 teeth 0.25" 
140 (Transmission gear) 0.96" 1.95" dia., 0.35" width, 20 teeth 1.49" dia., 0.34" width, 12 teeth 0.25" 
138 (attached to idler shaft) 0.25" 2.99" dia., 30 teeth n/a 0.25" 
128 (attached to motor) 0.25" 0.95" dia. 14 teeth n/a 0.25" 


Gear Comments: 

The measurements were taken with a vernier caliper (Starrett) ,and are only to the hundredths, due to the fluctuations in the plastic. Not having a metric tool measuring device to that precision, I could only measure in inches. 
Gear diameters are not precise, since the number of teeth is odd. The measurements were obtained by literally turning the gear between the jaws of the caliper and recording the maximum distance. Again, being plastic, there was some variation. 
The smaller diameter of p/n 140 is a 'best guess'. This gear is the one on back order, and mine is broken in two, with only 3 teeth remaining. I measured the hub as well as possible, measured the tooth height, then added that twice to the hub diameter. 
The gear height (distance from hub to edge) is rough and was taken from the tooth edge to where it 'appeared' the hub should be. 
The gear widths are different between the two sets. It is slight, but noticable. The high speed combination is thinner than the slow speed. 
I didn't measure the inside diameter of each gear, but I assume it matches the respective shaft diameters of 30mm for the spindle shaft and 12mm for the transmission shaft. The spindle gear (p/n 140) was a tight fit. The transmission gear (p/n 80) fit is looser, as it has to slide easily along its shaft. 
The motor gear to spindle gear (p/n 128/n 138) ratio is 14:30, or 0.47: 1. The high speed gear ratio is 21:20, or 1.05:1 . The slow speed gear ratio is 12:29, or 0.41:1 . 

Bearings Bearing Stock Part Number O/D I/D Width 
123 (Spindle) 6206-Z 62 mm 30 mm 16 mm 
139 (Idler Shaft) 6001-Z 28 mm 12 mm 8 mm 


Bearing Comments: 
The spindle and idler shaft bearings are single row, deep-grooved (or Conrad-type) double shielded radial ball bearings. They are stock metric bearings. 
This means that they are available from a number of sources. All you need to do is ask for this number or equivalent. If for the remotest of reasons you should ever need to replace them, they would be available from sources other than Grizzly . (I have a feeling the same holds true on the HF 7x10 and its 'clones'). 

Spindle Shaft 
The total length is about 167mm. The first 15mm or so is threaded 27 x 1.5 left-handed, for the spindle nut at the top. The next 122mm of length is 30mm in diameter and is what the gear and bearings ride on. The latter 30mm of the shaft is 40mm in diameter. This is the bottom portion which receives the collets. The lower bearing sits on the shoulder where the shaft goes from 30mm to 40mm. 

CHECKLIST 

Use the following checklist to document your progress: 




Task Name Step Number Completed/Comments 
SPINDLE ASSEMBLY REMOVAL 1  
 2  
 3  
 4  
 5  
 6  
 7  
 8  
 9  
 10  

SPINDLE ASSEMBLY DISASSEMBLY 1  
 2  
 3  

GEAR REMOVAL/REPLACEMENT:   
Idler Gear/Shaft Replacement 1  
 2  
 3  
 4  
 5  

Transmission Gear/Spindle Removal 1  
 2  
 3  
 4  
 5  
 6  
 7  
 8  
 9  
 10  

Transmission Gear/Spindle Replacement 1  
 2  
 3  
 4  
 5  
 6  
 7  
 8  
 9  
 10  
 11  
 12  

Idler Gear/Shaft Replacement 1  
  2  
 3  
 4  

SPINDLE ASSEMBLY REASSEMBLY 1  

SPINDLE ASSEMBLY REPLACEMENT 1  
 2  
 3  
 4


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