Improving Your Stubby’s Banjo
Posted on July 27, 2007
Improving Your Stubby With The Waldon Banjo Lock
Authored by: Don |
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Introduction
This material is the property of Walt and Don and you may use this material to build a lock for your use, provided that this material is in no way used for commercial gain. Please let us know by email http://www.turnedoutright.com/ how it worked for you and any suggestions you may have for further improvements.
Disclaimer
By using the information provided to you below you undertake the modifications at your own risk and Walt and I assume no responsibility either expressed or implied for any damage or loss of any nature at any time for any reason. Note: some of the modifications shown below may not be supported by your lathe manufacturer.
Get back to turning
I hope that our experience and these instructions on how to improve the Stubby’s banjo locking serve to assist you in getting the full performance of your Stubby. We believe and our experience has shown that these modifications create an improved and expectedly safer turning experience.
Do us a good turn, please
We ask only one thing in return for our hard work and effort. Drop us an email if you make this modification so we can keep a tally of how many lathes have been modified. Also let us know if it was worth the effort to you. Finally let us know if you agree with our view that these modifications should be put in the production units. We will pass a summary of everyone’s comments anonymously to Omega Tool.
Background
It wasn’t soon after I got my stubby in December of 06 that I realized that the banjo locking was less than what I was used to on the Jet that it replaced. For a week or so the performance of the lock was discussed on the Stubby forum resulting in mixed set of opinions on how to improve the lock as well as whether it needed improvements. Many suggestions were made for improvements including , a totally new design, increased shaft and stud sizes and cleaning of the ways. To be clear, not all users of the stubby deemed the locking performance to be a problem. However a few users considered the Stubby to be a “heavy duty” lathe and were dissatisfied with the “soft locking”. The desire to have a more positive and adjustment free locking motivated myself and Walt to go “offline” and continue our quest for a “better lock”. The Omega Tool Co. was contacted to determine if they were interested in collaborating on improvements to the lock. Omega did not answer our inquiry so the two of us set off to design, fabricate and test various improvements to the current Stubby banjo without factory assistance. We’d be happy if Omega would just implement these improvements into their standard production units but …………. if you agree email us and we will pass it to them.
Description of the condition & the motivation to improve
Many of the Stubby’s users noticed that the banjo locking was softer than expected. Soft means that as you lock down the handle there is a poor terminating position. Each time the handle was “hard locked” (forceful locking of the handle) the position of the handle would terminate closer to the 90 degrees down position, until it would eventually “go over center” and not lock. Readjustment of the locking nut on the banjo lock would restore the lock to its initial operation. Although it was not proven, it was feared that with enough cycles of “hard locking and nut adjusting” the locking stud would fatigue and the lock would fail. At a minimum the need to adjust the banjo nut was considered undesirable by us. 
After tests showed little camshaft deflection, it seemed apparent if the lock was not holding then there had to be a change in dimension or stability relating to the distance from the cam follower to the surface of the locking disk. We label this error “Z” for this discussion. The picture to the left shows the test set up. The flat sided bars simulate the ways which are pinched between the base of the banjo and the locking disk. It is our belief that “Z” becomes larger when the stock banjo is locked. An initial experiment with an extra nut improved the locks operation. It is still not precisely clear what was causing the variable Z but the extra nut led us to believe that the threads were distorting. In any case the Waldon design improved the banjo’s operation to our satisfaction. Note: their was allot of debate regarding the actual cause of the banjo’s soft locking. Bottom line Walt and I stopped debating and just fixed it. I really don’t care what the exact cause is, I just like my modified banjo.
The new design
Outlined below are the five main pieces of the design described using our own naming convention. In each section we summarize our finding, suspicions of defects and design changes.
Shaft:
The camshaft mounts horizontally under the casting of the banjo supported on each end by a Oilite sleeve bearing. The locking handle connects to one end of the shaft for activation. The cam follower sleeve is mounted over the camshaft. Clearly shaft defection could be a logical source of error Z. However we measured at the shaft throughout the cam rotation and found very little deflection so we concluded that this was not the main source of “Z”. We aspire to experiment with harder shafts later on.
Cam Follower
Since we did not see much shaft defection we did not imagine that the cam follower could deflect either. We did postulate that an increase in the thickness and length of the follower would improve it operation and also reduce shaft bending, if that really was a hidden factor. Since we were to replace this element anyway we decided to change its length and thickness.
Cam stud and nut
The cam stud is welded to the cam follower and serves to hold the locking plate below the ways. Two factors caused us to conclude that most of the distortion was coming from the stud- nut combination. First, early in the investigation the stud was suspected simply because of the large difference in stud size between the Stubby implementation and other implementations of the same design in other better performing banjo’s. Second, an early experiment showed that adding another nut to the stud, resulted in marked improvements in the locking performance. It was postulated that the threads on the smaller Stubby stud or nut were distorting/stretching and the increase in the number of threads created by the additional nut reduced that error. The Waldon design uses a 3/4 inch Grade 8 NF locking nut to minimize increases in “Z”.
Centering plate
This type of design uses a disk assembled on the shaft between the cam follower and the locking disk to guide the banjo in the ways. This disk is not under any force and was therefore eliminated from the investigation. One improvement that was not prototyped included the addition of a locking key-way in the centering and locking disk which interposed a corresponding pin in the shaft. It was judged that inhibiting the spacer disk and locking disk from rotating would reduce the ability of the banjo to move/rotate when locked. This concept has not yet been tested.
Locking Plate
The locking disk operates on the bottom of the ways and the cam pulls it upward to pinch the ways in lock. We believe that it is important for this disk to be hard, flat and as thick as practical. The Waldon locking disk is about 20% thicker than the Stubby implementation. As stated in the paragraph above we believe that a locking pin and key-way could improve the rotational locking plate performance of the banjo.
Testing
Walt and I both have locks installed and operating successfully on our Stubby’s. The locking performance is much superior than the stock design without any degradation in usability. I have my handle adjusted to 5 o’clock and since it always locks in the same position I find the banjo easier to use because the handle is out of the way. Both Walt and I are very pleased with the results.
Implementing the Waldon improvements
These locks were built by Walt in his shop but whether you choose to do it yourself or commission a machine shop we hope this information can help you like it did us. I am in process of getting quotes from local machine shops but didn’t want to wait until I have them to post this information. I will post the quotes when they return. You can obtain the prints from us and take them to your favorite machine shop. I also have someone that could make us a batch if the volume was high enough.The pictures below compare the factory stubby assembly and the Waldon redesign.
Simple Improvement
If you don’t want to go as far as have a new lock made then as suggested earlier, you can get a lot of improvement just by changing the nuts on your Stubby’s banjo. To do this:
1. Turn over your banjo and locate the 10mm locking nut
2. Remove this nut and replace it with two nuts tightened against each other in a locking configuration by holding one while tightening the other against it. Get the hardest and thickest nuts you can find for each. Don’t use two locking nuts as in the picture, this was all I had for the experiment. Use a locking nut on the top and a non-locking nut underneath. If you do this to the auxiliary banjo you may need to remove some of the web on the aux bed so this nut can clear.
Implementing the improvement
If you are building or having a lock built let us know by emailing mailto:don@turnedoutright.com so we can keep track of the interest. Drawings for the lock can be downloaded here. Both PDF and .skp versions are available.
Waldon lock drawings (pdf) Sketchup generated drawing as an image:
A Sketchup 3D model is avialable by emailing me. Note: Sketchup is a free Google drawing software and is available at http://www.sketchup.com.
Instructions for removing and installing the lock.
All the tools you will need are shown below:
- Hammer
- Shop made bearing removal tool
- Punch
Turn the banjo over and mark the shaft in a way that you can return the handle to its original position. I used a Sharpie to mark the shaft in on the side of the shaft opposite that of the handles ball.
Using the punch knock out the pin holding the handle to the camshaft. Keep the pin.
Tap the bushing out carefully using the removal tool. Remove the shaft and old lock.
Slide the shaft back into the banjo through the new lock
Tap the bearing back onto the shaft using bearing removal tool.
The banjo with the new lock installed, note the orientation of the handle to the dot on the shaft
A picture of Walt’s removal tools
Making the bearing removal tool
I built my removal tool by welding a piece of hand cut 1″ tubing to a 1/2″ CRS steel rod. Choose a piece of tubing whose wall thickness is equal to or smaller than the bushings thickness. Mine came from an old shower rod. Weld this perpendicular to the shaft at one end. I suppose we can share the tool I made if you don’t have a welder but I don’t want to get stuck with shipping it and tracking it down. Suggestions are welcome for those without a welder.A .pdf of my removal tool design below: bearing-removal-tool.pdf
Modifications to the Stubby’s auxiliary bed
You may need to modify the webs in the auxiliary bed if you want to adapt your auxiliary banjo to the Waldon lock and or use your primary banjo in the auxiliary bed. If you don’t want to use the Waldon lock and/oror your tailstock in your auxiliary bed then no modifications are necessary. Caution: The lathe modification in this section are NOT supported by Omega Tool so you make them at your own risk. However, these changes in our opinion in no way compromises the integrity of your lathe, but you should make your own assessment. It seems that our lathes have auxiliary beds that were machined to different dimensions or not at all. Omega’s position is that the auxiliary bed was not intended to accept the tail-stock and that the banjos are not interchangeable. This doesn’t make sense to us. The inside surfaces of the ways are machined on the main bed, not machining the surfaces of the Aux would make the floating plate grab so why aren’t they also “OFFICIALLY” machined. It probably does grab, its just that not many of us use the AUX than much to have it be a problem. Omega Tool doesn’t seem to appreciate that many of us bought this lathe for its flexibility and that many of us use the tail-stock for mounting boring and other tools. Not being able to exchange tail-stocks and banjo’s unnecessarily limits the Stubby flexibility. If your were unfortunate enough, like Walt and I, and your bed was not machined at all to the correct dimension then I suggest you investigate having it machined at the same you have your lock made. Without this modification your tail-stock and the Waldon lock might not fit into the auxiliary bed. Walt fixed his aux bed himself and I’m sending mine to a machine shop. We cannot give you specific instructions for modifying the beds because not all are the same, but the modifications are not difficult to comprehend. 1. The aux “ways” may need to be widened slightly to accept the centering plate in the Waldon design if it is not the same size as the main bed. Alternatively you can have a special centering plate made to fit he AUX with the disadvantage that the banjo’s are not interchangeable. 2. The locking surface (under the ways) may be a different size than the main bed. I don’t know how difficult this is to machine yet. Choices are: make a special locking plate for the aux banjo sacrificing its interchangeability. 3. The longer bolt and nut on the Waldon lock may catch on the web in the aux bed. A small amount of material may need to be removed to provide clearance. A grinder works fine or have this done while machining.
Below are photos of my lathes measurements as an example.
The main beds gap (1.9480)
The AUX beds gap (.02 narrower because the measured surfaces are not machined). Note the web in the top of this picture it is the one that may need grinding for the new locks bolt to clear.
The main beds locking surface (3.13).
The AUX beds locking surface (.380″ smaller). Unless I machine these surfaces, mine will require a smaller locking plate than the main bed and my banjo’s won’t interchange :(.
Note: Walt’s locking surface is 3.125″.
Walt’s setup for shop grinding the aux bed is shown below.
