Bushing with a Mill - Clarifying the Process

[Ninjak2k]

I was hoping to clarify a few points about the bushing with a mill process discussed by Jerry Kieffer and others on this board. This is for regular bushing job, not fixing a bad bushing job that was already done. Here's the process as I understand it with questions intermixed.

1) You find the correct location with a pin gauge the same size as the pivot on the gear. You do this by moving the gauge in the hole to the point the pivot should have been in the oblong hole, with a magnifier if necessary to precisely position it. No filing or center finder is needed since the pin gauge is the same size as the pivot and you can locate it in the hole by sight.

2) Keeping the table stationary, replace the pin gauge with the necessary reamer and ream out the hole. I believe at least one forum member recommended starting with a smaller reamer and increasing to the proper size; is that recommended? Another mentioned running the reamer with the motor at the lowest setting (25 RPM for them), but I noticed the specs on the Sherline site (which is the mill I'm looking to purchase) state the motors go from 70 - 2800 RPM. Is 70 RPM too fast for reaming and should it instead be turned by hand? Do you just slowly plunge it into the plate?

3) Do you use a chamfer tool to debur the hole afterwards? Do you do both sides of the hole of just the inside of the plate, the side the bushing is inserted on?

4) Replace reamer with a ram (or can a punch somehow be fitted to the mill?) and push in bushing. Some have said they prefer to install the bushing on a ground plate outside the mill. Do most prefer doing this by hand?

I was looking at the Sherline 2000 mill just because I don't know if I'd ever need the ability for the other directions of movement. Can you think of any reason they would be needed for clock work or watch work?

Would you recommend DRO readouts over the standard handwheels?

Cheers,
Dan

[harold bain]

Hi, Dan. I think your question is more likely to attract the attention of Jerry and others in the tool forum, so I am going to move it there for better exposure.

[David Robertson]

Dan,

I don't use a Sherline, but do use a tabletop mill to bush. I deviate a little from your posted procedure..

The pin gage I select is the largest that will fit in the hole, not the pivot diameter. This way the gage pin will only fit in the original hole and there is no precise visual alignment needed.. you align visually and then tweek the table location until the pin will go down in the hole without hanging on the edge.

I use a bottom cutting end mill slightly smaller than the reamer I will use to cut the bulk of the hole. I could do it all in one step with the reamer, but I have a small mill paired with each standard reamer and it just takes a few seconds longer to use both vs one.

The mill I use will virtually go to zero rpm so I go very slow.

I hold the tools with an Albrecht chuck.. very little runout.

I have a couple of clamps that hold the plate from two sides and a moveable stump that I place under the plate at the point of interest to provide stability.

I push in bush external to the mill.. on a bench block with a small hammer.. or sometimes with a small arbor press.

Picture attached.

[Ninjak2k]

Jerry was kind enough to respond to a PM of mine with the same questions, so I won't make him repeat himself:

Originally Posted by Jerry Kieffer

I will answer in order by number.

#1
You are correct. However you can use a Pin Gage as suggested or a Drill shank, stacking tool punch or whatever will do the job for you. For those bushings that are not critical you can also use a bushing reamers tapered tip.

#2
The first part is correct. However I use a standard bushing reamer to ream the hole for the proper matching bushing. Only one pass is made to ream the hole. With this system it can be done by hand or under power. When under power I do it at the slowest speed that is about 25-50 rpm by my best guess. Either way it is moved slowly into the plate untill you get use to the system.

#3
No


#4
Personally I ream all required holes in a plate and then bush on a ground surface. This allows me to stack a bushing so it will not come out as well as dress both the top and bottom surfaces.
If I wish to bush with the mill I use a punch down the center of the spindle and tap the bushings in place. When I do this I ream all holes first and then go back and bush all holes. Since location for bushing is not critical, relocation of the spindle for bushing is very fast. A support is also used under the plate when bushing.


The 2000 Mill is a great mill but I have not found a need for any Sherline larger than the 5400 Mill for Clock and watch work. Another words if you need a larger Mill than the 5400, then you also need something larger than the 2000. Sherline equipment will handle anything from the smallest watch work up to a typical English Grandfather clock movement.


Sherline Leadscrews are very accurate and the handwheels are clearly marked. The only advantage in my personal opinion for the DRO is the large readout. Another words many people cannot see handwheel markings or prefer a large readout for whatever reason.

[Jerry Kieffer]

Dan
I responded to your PM on this subject, but will respond here for anyone who may have an interest.

My first use of a small mill for bushing was for fast and simple correction of bushings that were installed out of proper position. Since then I also use it for general bushing because for me personally, it is faster and far more accurate than other methods including bushing machines. The plate is clamped in place on blocks and a gage pin (or whatever) is mounted in the spindle in a WW collet of the same size as the pivot.
The pin is the easily positioned in the correct pivot hole location by moving the slides. This gives fast, accurate location without reclamping the plate for as many holes as required on that plate. When located, the gage pin is removed and the bushing reamer is installed also using WW collets. Personally I only use a bushing reamer or whatever is required for a special size hole. When using WW collets or a accurate keyless chuck as mentioned by David, the change is very simple and fast for each hole. I ream under power at a slow speed (25-50 rpm) and advance slowly through the plate.
Personally when the holes are reamed I remove the plate and stake the bushings on a ground surface as well as dress as required. However bushings can be installed in the mill by tapping into place with a rod down the spindle and support under the plate. If I do this I first ream all holes and then bush all holes. I have found this to be the most efficient when using this method.

Reaming can be done under power or by hand. All of my variable speed machines including Sherlines will operate down to at least 25 rpm for this type work.
Again personally I have found that work that will not easily fit in my standard size Sherline mill (5400) and other small mills that I own, is better done on a larger Mill. Envelope dimensions should be available forwhat ever brand is considered.

DRO,s seem to be a personal preference thing. Personally I have them on all of my larger machines but not my smaller machines. On small machines I like the the use of clearly marked handwheels and the feel of what is going on without distraction. But again this is a personal preference.

Jerry Kieffer

[Jerry Kieffer]

David
The use of Lathe tool post holders for holding plates in the Mill is an excellent idea when only bushing is required. (Per your Photo)

For whatever reason it never occured to me.

Thanks
Jerry Kieffer

[David Robertson]

Thanks Jerry..

I was going to make some of the "E" shaped ones like you have but I didn't want to take the time so looked around for something in the shop that would work..

Haven't really seen a need to improve upon the system so far.

BTW..They are Taig tool holders and are very inexpensive (less than $5 each).. but any kind would work.