Mark VII Gear Rack Replacement

[redleg]

Recently purchased a sixties vintage Mark VII. I had seen a Mark V demo in the early eighties and had always wanted one but when I started looking for a used Shopsmith about eight years ago I initially thought a Mark VII would be a model newer than the Mark V. Go figure though it was older so I bought a Mark V with a bunch of SPT for a good price. Knowing what I know now I probably could have gotten it for a $100 less. Anyway the Mark VII was rough, the headstock sounded like a plane crash landing on the runway when the owner turned it on. The gear rack was shot and no telling when it last saw a drop of oil. He wanted $500 for it and I gave him $175 yes a high price but it had a mortising attachment and a rack of shaper bits worth at least a hundred used. The problematic speed control was in really good shape so I figured I could get my money back on parts, use the headstock from my 84 Mark V and convert the Mark V to a SPT mini storage stand. When I tore into the headstock back at home I found a piece of the gear rack was wedged between the headstock case and the sheaves. Took that out cleaned and lubed the inside and it purred like a kitten so I decided to fix it. First step was the infamous broken gear rack and clean the way and bench tubes while I was at it.

[ATTACH]21529[/ATTACH]
Miter gauge with rack jig similar to the use of a finger joint jig.

[ATTACH]21532[/ATTACH]
Rack teeth cut with a 1/4 inch double ended 45°/60° router bit. I had to grind the point off the end of the bit for the flat bottom between the teeth. I tried to measure the angle on the old rack teeth but with only a sliding bevel and a speed square I came up with 18° questionable versus the 22 1/2° with the new one based on the 45° end of the router bit half of which is 22 1/2°.

Lost a picture of the routing of the back side of the rack. Ran the rack through the bandsaw to get it to the right thickness. Used a ZCI on the table saw made by running a 3/8 inch core bit up through it. Offset the router bit from center of the back side of the rack and ran the rack through twice flipping it end to end and leaving about 1/16 inch on the outside edge. I set the depth using a piece of the broken rack.

[ATTACH]21530[/ATTACH]
Old and new rack parts closely match.

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Making a drive insert for turning the tubes. Used a countersunk bolt with washer, lock washer and a nut. Bolt extends about an inch into drill chuck. Taper the drive insert so that it goes into the tube at least an inch. Use a round file to remove the burr on the inside of the tube before inserting. The other end is turned similarly but without the bolt.

More to come another day.

[BuckeyeDennis]

Wow, that is some creative fixturing and problem-solving! I'd love to see more of it.

[JPG]

Wow, that is some creative fixturing and problem-solving! I'd love to see more of it.

I'd love to see more details re the 'tooth bit' and the 7/8" back radius cut.

Oh and what/where for the 'raw material'.

[redleg]

I'll get some close ups of the bits. The 45 degree/60 degree was from a Craftsman router bit set. The material was an old food service cutting board I think polyethylene plastic. It might be too soft but I'll see how long this lasts and then spring for something that isn't free. I'm not an engineer so if someone has a reasonably priced alternative material in mind let me know. The back cut was just an UNSWAG based on a visual of the original.

[ATTACH]21540[/ATTACH]
Sanded 100 to 400 grit, cleaned, and waxed the way tubes and lightly caressed the bench tubes with steel-wool and waxed while turning on the Power Pro.

[ATTACH]21541[/ATTACH]
Newly installed rack. I was surprised when I found that the original rack was made in two pieces and pop riveted to the way tube. I used a small electrical wire crimping sleeve between the rivet gun and pop rivet to keep the head of the rivet gun out of the teeth.

[ATTACH]21543[/ATTACH]
Mark VII back together.

[ATTACH]21542[/ATTACH]
The headstock and carriage can lock together so they move as one unit.

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I ran the headstock and carriage up and down several times in the vertical position. Shown here vertical not locked down and full weight on the rack teeth.

[redleg]

[ATTACH]21555[/ATTACH]

The two bits I used both from Craftsman sets 45°/60° bit part number was 9-25545 (probably around 20 years ago) the other was a little more modern carbide tipped 3/8" core bit (corrected in earlier post). The core bit was used with the table fence and shop made ZCI for the back side of the gear rack.

[db5]

Those are NOT the tubes I sent you! I really liked that the carriage and main table can be moved as a unit. I do not understand why SS has never incorporated this.

[JPG]

Those are NOT the tubes I sent you! I really liked that the carriage and main table can be moved as a unit. I do not understand why SS has never incorporated this.

They did in the Mark VII. SS Inc. ran with the Mark 5.

You had more than one set of Mark VII tubes?;)

[JPG]

[ATTACH]21555[/ATTACH]

The two bits I used both from Craftsman sets 45°/60° bit part number was 9-25545 (probably around 20 years ago) the other was a little more modern carbide tipped 3/8" core bit (corrected in earlier post). The core bit was used with the table fence and shop made ZCI for the back side of the gear rack.

I think I would be more inclined to call that a 45/30 degree bit and a 3/4" cove bit.

[rcplaneguy]

It has been over 6 months, how is the plastic rack holding up? Any problems?

[redleg]

Sorry to say I parted with the Mark VII. I used it for a while and had no problem with it. Hopefully the new owner monitors the forum and will chime in. It had some great features that I wish Shopsmith had included with my Power Pro. EDIT: 12-30-2013 I spoke with the new owner of my old Mark VII today. He stated that it cranks fine on the rack but it pushes hard when the clutch is disengaged. I offered to give him another gear rack that I'm making but I got the impression that he doesn't use it a lot.