Singer 29K70 Gearbox Inspection

[Snakeoil]

Went back into the gearbox today to revisit what I thought was a worn bore for the drive pinion of the shuttle drive. Figured I'd do another blow by blow for those who have never done this before.

First, take the machine off the treadle base if you have one. For stand alone machines just flop it over onto it's back side. Put a piece of wood under the top arm to keep the weight of the foot lift lever. Don't try to go into the gearbox with the machine standing up in the stand because things will fall out or worse, launch out and it is very difficult at best to reassemble the components in that position.

Before we get too far, this is a good place to mention good screwdrivers.

I also do gun smithing as a hobby and good screwdrivers are a must have to avoid buggering up slotted screws on fine firearms. Here is a set that I would recommend to anyone that works on sewing machines or other fine machinery that uses slotted screws. The tips are all hollow ground which means you can alter them to fit screws, or re-sharpen them if they get damaged. I got these from Brownells. Not the little ratchet wrench handle. Very useful. You'll see that used later.

With the machine lying on it's back side, remove the two screws for the cover plate. These have very shallow slots so use a screwdriver that properly fits.  Keep figure pressure on the plate as you remove the screws. I suggest you remove the left screw first. Then the right. Keep the plate in place with your fingers because there is a spring behind it.

With the screws removed, ease off on the plate and set it aside. This is what you should see.

See that spring on the right? That keeps the needleplate locating pin pushed up. This is one of the parts that would try to escape if you had taken the plate off with the machine upright.

Remove that spring and then either push out the pin from the other side with an awl or small punch. I use a small magnet to remove it.

Here is the gearbox with the plate removed. The two pinion gears and racks may be in a different position. It does not matter. But this is how you will position them when you reassemble the gearbox.

First order of business is to remove the lower rack called the Short Rack. It will simply slip out. This is most easily done with a magnet. The remove the Following Pinion, which is the gear on the right. It too just slides off its shaft.

Unless you are doing a full strip down, the Long Rack can stay in place.

Here is the gearbox with the Short Rack and Follower Pinion removed. The small screwdriver, which has been ground to fit into the slotted Pinion Screw is shown. Note that the Long Rack has been moved to the right a bit by turning the handwheel. This allows you to rotate the Driving Pinion so that the Pinion Screw is aligned with the hole/slot on the back of the gearbox. Make sure your screwdriver fits that little screw. If you destroy the slot with a bad fitting screwdriver, you are in for a lot of mental anguish in getting that screw out. You will see why in the next photos.

Continued in next post.

[mikesc]

Again ..Thank you for the thread .. :)
btw..superbly clear photos ..

[Snakeoil]

The Pinion screw goes thru the Driving pinion into the shank of the Shuttle Carrier. It is not a set screw. It is more of a threaded pin. I would expect it to be tight. Mine way. This is why it is so important to take the time to fit a screwdriver to this screw, both on a width and thickness basis. You don't want the screwdriver to be too wide and stop on the ID of the Drive Pinion screw hole and make you think it is bottomed in the slot for obvious reasons.

Here is the Pinion Screw. My slot was already beat up.

Here is the screw on my screwdriver. Note how deep the screwdriver is into the screw slot. It is deep enough that the screw hangs off the end of the screwdriver. This is what you want.

Here is my screwdriver inside the screw hole of the Driving Pinion. Note that it passes all the way thru. Again, this is good thing.

Here is the Shuttle Carrier. This is the side of the shank where the screw enters from the Driving Pinion.

Note that the hole goes all the way thru. Hence my calling it a threaded pin. But also note that on the other side the hole is smaller. Something to keep in mind during reassembly.

Getting back to why I took the gearbox apart, the first time I did it, I thought that the fit of the Driving pinion shank to the bore in the gearbox was worn. I wanted to see how much and if I could make a bushing or find another way to restore it. I also thought at the time, that the bore was simply that, a bore directly drilled and reamed into the gearbox itself. Turns out that is not true. There is a steel bushing pressed into the gearbox. This makes it rebuildable by installing a new bushing. However, I measured the shank on the Driving Pinion and the bore of the Pinion Bushing and there is about 0.001" clearance. So, I would think this is fine. 0.0005" might be better. But I'm okay with 0.001"

 

Edited February 23, 2020 by Snakeoil

[Snakeoil]

Here is a pic of the bushing. Note that this bushing is not shown in the 29K70 Parts Diagrams. But it is show in the 29K71 Parts Diagrams. I'm wondering if my machine was rebuilt with a K71 gearbox or if later K70 machines had many of the K71 upgrades/features. The part number for that bushing is the K71 part number.

So, let's put it back together. You can refer to the photos above for the reassembly process in addition to what I post below. The site is limiting me in how many photos I can post. So, it looks like I'm done with any new photos. But I think we have all we need anyway.

First, put the Shuttle Carrier in place and slide the Driving Pinion onto the shank of the Carrier. Make sure you light up the threaded pin hole. The big end on the Carrier shank should face the hole in the Driving Pinion. I would start the screw a thread or two into the pinion before you assemble the two parts. The slot/hole in the gearbox will give you clearance for the screw sticking out of the pinion. Carefully screw the Pinion screw into the Driving Pinion and Shuttle carrier. Go easy. If it stop rather than enters the Shuttle Carrier, recheck alignment or twist them a tad relative to each other until the screw threads into the Carrier shank. If you force it, you will ruin the screw. No ham fisted machine techs allowed here!!

With the screw home and snug, and snug mean snug, not Harley axle bolt tight, turn the pinion until it is position as in the photo above showing all the parts installed in the gearbox. Rotate the hand wheel until the Long Rack is just entering touching the Driving pinion. Then insert the Following pinion onto its shaft with the flat side of the pinion facing the cover plate (down). With that in place, insert the Short Rack and the gearbox is now assembled. It should look like it does in that same photo. Note the symmetry of how the parts are arranged.

Now insert the Needleplate pin, which is called the Locating Plunger into it's hole with the pin end upward. Push it all the way in and then insert the spring behind it. If you did not oil parts while installing them, give all the parts a good squirt of oil. Now position the coverplate over the gearbox and align it so the Following Pinion shaft come thru the hole in the coverplate as you compress the spring and place it tight against the gearbox. Insert the right screw while holding the coverplate in place and snug it up. You can let go of the coverplate now and insert the other screw on the left. Just snug those screws. You are done!

I was going to show you how to use that little Chapman ratchet handle but the site limit has been hit for photos in a thread. So, I'll start another thread about removing my head and show you there.

regards,

Rob

 

Edited February 23, 2020 by Snakeoil

[Constabulary]

Once again - excellent read! Its great that you show all the details.

Your gearbox pinions & racks really look good. Could well be that the machine has been rebuilt. The 29K70 pretty much is a 29K71 - If I see it correctly the 29K70 is more or less a 29K71 with a different thread lever adjuster and some 29K70 seem to come w/o the front crank setup. Not sure which 29K70 parts list you have but this one shows the bushing (see attachment - plate 7745).

Parts List Singer 29K70.pdf

[Gunnarsson]

Very interesting. And I notice that the tooth profile appears quite different from the 29K4 and other early machines, the teeth on the racks ( but not gears) have straight edges here (like a V) while the older machines have teeth curved sides on the racks as well as the gears. Perhaps a involute profile here and a cycloidal gear profile in the old machines. (The kind of things you start paying attention to when you think about how to make new gears to machines where parts aren't available.)

[Constabulary]

The pinions are totally different. 29K4 have a lot larger pinions and they are not interchangeable. The 29 / 29K series used at least 3 different type of pinions - I can post  pictures  later.

[Wizcrafts]

1 hour ago, Constabulary said:

The pinions are totally different. 29K4 have a lot larger pinions and they are not interchangeable. The 29 / 29K series used at least 3 different type of pinions - I can post  pictures  later.

People buying ancient Singer 29-4 and other models from the early to mid 20th Century find that out when they buy aftermarket gears that don't work.

[Constabulary]

53 minutes ago, Wizcrafts said:

People buying ancient Singer 29-4 and other models from the early to mid 20th Century find that out when they buy aftermarket gears that don't work.

True!

 

Just to give an idea what pinion you find among the 29 / 29K series:  From left to right:

• Pinions for approx 29-1 / 29K1 - 29K33 (there could be differences too but this is pretty much the size)
• Pinion for 29K51 - 29K56
• Pinion for 29K58 - 29K73 (and higher I think)

The 29K58 - 29K73 pinions are the ones you can buy new - the other pinons are no longer available new. Well you may find them but they are out of production for decades! Sometimes you find them used on Ebay but buying used pinions is not a good idea.

However - I think (but I´m not sure) that the large pinions are approx the same they use in the Adler 30 class - they never have changed their pinions AFAIK but I´m not 100% sure. I haven´t had the chance to test then 1:1 coming from a working Adler 30 and Singer 29K gear box - maybe one day... I´m curios...

Beside the pinion sizes, in the 29K series there are gear boxes with 3 pinions and 1 long drive rack and gear boxes with 2 pinons 1 short rack and 1 long drive rack... you have fixed gear boxes (29K1 - 29K33), drop out gear boxes (29K51 -29K56) and fully replaceable gear boxes (horns) 29K58 -29K73 and higher)... Looots of differences.

Some 29K series gear box samples - the latest model is shown above so there are at least 4 different gear boxes

Edited February 23, 2020 by Constabulary

[Gunnarsson]

2 hours ago, Constabulary said:

The 29K58 - 29K73 pinions are the ones you can buy new - the other pinons are no longer available new. Well you may find them but they are out of production for decades! Sometimes you find them used on Ebay but buying used pinions is not a good idea.

This is the cause of my interest. If I ever get my hands on a 29 it'll probably be an old worn one, and research has said that these parts are often in more or less bad shape and new replacements are not available - as you have confirmed here.

However, gears with straight cut teeth (pinions) and straight racks are relatively simple items to make. You need (preferably) a mill, a device to rotate the gear blank and lock it in the precise positions for each cut, and a cutter with the right shape to cut teeth with the profile you want. The rack should be even simpler, as it's a straight motion between each cut, not rotation, but you need the correct shape cutter for that too. 

For "modern" involute gear profiles, at least for 12 tooth and up you can easily buy the cutting tools assuming it's a standard size. In the pictures it looks like the 29K51 and higher has this style of teeth. The earlier ones however seem to use a different profile, and that wouldn't be a surprise as it's a rather old mechanical device, people were still trying to figure out what was the best type of gear etc. The downside to this is you need to figure out what shape the teeth were before 100 years of wear if you want to make fresh copies (or you need to redesign it and make a kit of all new parts that only will work with each other).
As for buying the right cutters you can probably forget about it, but you can grind HSS to the proper shape. But to get there you either have to figure out what system the gears were created with and "do the math" to come up with the shape to aim for at the grinder, or find a NOS set of parts to copy (and hope that the production tolerances on that day were good, so the NOS gear actually is close to perfect). 

Might as well ask: are the pinions and racks hardened, or are they made from softer mild steel?