A Real Dirty Job

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Carrdo
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Re: A Real Dirty Job

Post by Carrdo » Sun Oct 28, 2018 6:42 pm

Two leaf spring bundles consisting of 12 leaves each and twenty five bronze leaf spring spacers (which are 3/8" OD by 1/8" ID by 3/64" thick). The Langworthy drawings show the finished leaf springs, as assembled, so it was necessary to first do a bit of trig. to determine their initial flat (unbent) length.

Previously, I have described elsewhere here on Chaski how one can produce highly accurate (parallel face) thin washers of any size so I will not comment on how they were made.
Attachments
183 Two Leaf Spring Bundles and Bronze Spacers.jpg

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Carrdo
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Re: A Real Dirty Job

Post by Carrdo » Mon Oct 29, 2018 9:50 pm

The drilling of the center hole in each individual leaf spring.

It can be done successfully using the sandwich method which I have shown elsewhere on Chaski but this method is a bit time and material consuming (good for one or two holes) but as I have a total of 12 center holes to drill for the leaf spring center post in each leaf spring bundle and as there are a total of two bundles... But the sandwich method will work if one has HSS drills only (they need to be sharp).

Hard blue tempered spring steel is really miserable material to drill, so one has to know the tricks involved.

The center hole in each leaf spring has to be truly centered both lengthwise and on width which is a challenge to begin with.

Since I do everything without any digital aids, in the first photo one can see the 3/8"OD by 1/8" ID by 1/4" thick made up drill bushing which was used to locate the drill on width. Secondly, each spring leaf was left 1/16" longer than its finished length so that I could use a graduated scale and eye loupe to locate the drill lengthwise on the leaf spring and still be off a little bit which wouldn't matter at this stage.

Locate a leaf spring on top of the supporting 3/8" wide spacer so that the leaf spring rests just below the top of the vise jaws. This is necessary as one has to clearly see what is happening at all times. Ensure that everything is clamped rigidly. The supporting spacer (as seen in the third photo) has a special feature as it has a clearance hole drilled in it which is just a tiny bit larger than the hole in the leaf spring will be. There is a reason for this.

I also used the drill press for this operation as it was relatively easy to set up and make the necessary location adjustments. It also has a much higher speed than the mill and for this operation one needs speed.

Don't even try to center or prick punch this material as the punch will just skid around leaving a real mess.

Note the 1/8" dia. starting drill in the first photo. It is a solid carbide spade drill for sheet metal drilling and this is what one needs to begin. They are relatively expensive and easily damaged and sooner or later, with this material, they will micro chip on their cutting edges and break so one needs to do everything to preserve them.

Pierce the spring steel with the solid carbide spade drill at high speed by touching the surface of the spring steel with the tip of the drill and then slowly and evenly increase the drilling pressure until the drill cuts down to about 2/3 rd's of the drill diameter. Ensure that the drill breaks through into the space drilled into the supporting spacer. These drills are not designed to drill out solid material and if the spacer did not have the clearance hole, the carbide spade drill will chatter badly and that will be the end of the cutting edges on the drill. Also, you do not want to shock the carbide drill (as the drill breaks through the spring steel) by drilling through at full depth.

Now, switch to a sharp 1/8" HSS drill and complete the drilling (as seen in the second photo). The HSS drill will now have no problem completing the hole and it will be a clean, burr free, circular cut (as seen in the third photo).
Attachments
184 The Start of the Drilling of the Individual Leaf Spring Leaves.jpg
185 The End of Drilling an Individual Leaf Spring.jpg
186 After Drilling.jpg

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Carrdo
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Re: A Real Dirty Job

Post by Carrdo » Tue Oct 30, 2018 8:40 am

One thing which I forgot to say in my last post was when drilling with the carbide spade drill, keep the projection of the drill from the end of the drill chuck jaws as short as possible. Maximum rigidity of the spade drill is essential.

I should follow my own advice as the spade drill projection shown in the first photo could be a lot less.

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Carrdo
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Re: A Real Dirty Job

Post by Carrdo » Tue Oct 30, 2018 7:41 pm

All of the center post holes drilled.

No drill casultities.

In the end all very routine although contrary to my earlier post, the 1/8" dia. carbide spade drill seemed to drill best at the lowest speed on the drill press (700 rpm).
Attachments
187 All of the Center Post Holes Drilled.jpg

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Carrdo
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Re: A Real Dirty Job

Post by Carrdo » Sun Nov 04, 2018 10:21 pm

At this point I could just press on and bend the ends of the leaf springs as per the Langworthy drawings as seen in the first photo.

For completeness, if you can't read the drawing notes, here is what they say:

3 bottom leaves full length
Each succeeding leaf 1/4" shorter
2 springs, 12 leaves, 3/8" x 0.015"
Blue Spring Steel

and

12 brass washers 3/64" thick
2 leaves between bottom washers
One each succeeding washer

Using some trig and the 3/8" vertical offset shown on the print, the flat (unbent) length of the bottom leaf was calculated out at 2-7/8".

Note that due to the washer spacers, the bottom leaf is bent the least (it works out to just under 15 degrees) while as you move up the leaf pile the upper leaves have to be bent more to have the ends touch as shown on the print.

And the Josslin Hudson drawings show something similar with just with fewer leaves drawn (six) but drawn thicker (however, no thickness dimension given on the print so ???), thicker drawn but undimensioned spacers so ???, nothing to show how much the leaves are bent so ???

Now have a look at the real thing as seen in the second photo. This photo is taken from a publication on the rebuilding of a Reading Northern but the lead truck shown is very similar to a Hudson lead truck.

Notice:

The spring leaves are completely curved rather than having bent arms,

The greatest curvature is on the longest bottom leaf, the shortest top leaves having practically no curvature at all which is completely opposite to the model spring design,

No spacers, the individual leaves lay completely against one another and are tightly bound together. I do know why spacers are used in model designs - to give more springiness and to practically eliminate the sliding friction between the spring leaves as, due to the scale effect, the weight on model locomotive springs especially in the smaller gauges is miniscule compared to full size.

Trying to find out the why of all of this, the only model article I have ever come across is one by Henry Coventry in the February- March issue of the 1938 Modelmaker (third photo).

Henry tries to explain, in simple terms, how leaf spring sizing is arrived at on a model locomotive. He gives several formulas and an example calculation (suitable for a 3/4" scale locomotive). Where his formulas come from and what goes into the numbers he uses, I have no idea - the results look reasonable given my engineering background but are the numbers correct- that is another story entirely!

Also, for inch and one half scale Chet Peterson"s (Railroad Supply) technical handbook on model locomotive design contains a section on leaf spring sizing. Again, formulas and numbers appear which produce leaf spring sizes but what are they based on - again no explanation.

So, do I just go with a proven design or ...???

Take a look at the 4th photo. It is of Richard's Boston & Albany double ender. I have driven this locomotive several times and it is very stable on the track. The photo shows the engine springs as the lead truck uses 4, 3/8" diameter coil springs - no leaf springs there at all! The B&A double ender is really a cut down Hudson so the two designs are nearly the same although, in full size, the lead truck suspension on the B&A was connected through to to the engine suspension while on the NYC Hudson's, the lead truck suspension was independent of the engine's suspension.

The springs on the model are very close to full size practice as one can see. I have measured all of the relevant dimensions, size, curvature, number of leaves, spring steel thickness, width, the length each succeeding leaf is shorter than the one above it, top and bottom leaves are double, etc.etc.

This leaf spring design certainly did not come from the Yankee Shop drawings as originally supplied with the B&A - those drawings are pathetic to say the least. I think that they came from Al. Grigg who constructed a museum quality model of the B&A as Harry Hawkins (the original builder) and Al. knew one another quite well.

PS - the Al. Grigg model itself is not a Yankee Shop model as the casting all came from H. Allin who also built a magnificent B&A double ender in 3/4" scale.

Based on the spring measurements in Richard's engine, I then produced the leaf spring curvature calculation as seen in photo 192 and from that the full size layout on a plywood sheet, photo 193.

Other than wasting a whole lot of time on the above, I compared the leaf spring design on a Coventry Pacific which I also have and there is no resemblance to anything on any of the Hudson design's which I have or the B&A. The Hoffman Hudson also uses coil springs on the (simplified) lead truck.

So, all I would like to ask is there any additional useful information available which you know of on the design of leaf springs for model locomotives?

I know that Dave S.(Trainman) doesn't think much of working leaf springs but I do if properly designed but I haven't seen much useful information in this aspect of model locomotive construction to date.
Attachments
188 Langworthy Print of Lead Truck Leaf Springs.jpg
189 Full Size Lead Truck Spring Bundle.jpg
190 H. J. Coventry Article.jpg
191 Richard's B&A Leaf Springs.jpg
192 Leaf Spring Curviture Calculation.jpg
193 Full Size Curviture Layout on Plywood Sheet.jpg

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Carrdo
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Re: A Real Dirty Job

Post by Carrdo » Mon Nov 05, 2018 11:55 am

While dealing with the leaf spring issue, I spotted another major problem with both the Langworthy and Josslin Hudson lead truck designs. This had escaped my notice for decades. It is serious.

On both of these trucks (and the Josslin is by far the worst in this respect), the full vertical travel on the axleboxes cannot be realized as the top of the side equalizers jam up on the sloped underside of the brake lugs cast into or silver soldered onto the truck frame which severely limits axlebox vertical travel.

The problem can be solved by modifying the shape of the side equalizers in the area of the brake lugs or by cutting out more frame material where the brake lugs join the side frame (not my preferred solution) but to do this both trucks have to be completely taken apart again.

This is an example of where model design differs from full size practice as axlebox vertical travel on a model needs to be more than on full size.

Now I can see why there was so little leaf spring flex - there couldn't be as the side equalizer problem also prevented spring travel.

On less detailed lead trucks, not having frame brake lugs, one would never encounter this problem.

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Carrdo
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Re: A Real Dirty Job

Post by Carrdo » Mon Nov 05, 2018 6:53 pm

Using the G.H. Thomas workshop bending rolls to form the leaf spring continuous curvature on a bottom leaf spring. With these rolls the leaf springs can do nothing other than what you want them to do.

You can put a leaf spring through the rolls over and over again reversing it lengthwise in seconds. And the leaf spring will not kink at the center hole location (which is now a weak point on the leaf spring) as the leaf spring is fully supported between the two large pinch rollers and the smaller forming roller when the spring steel is fed through the unit. What a well thought out and versatile design.

Decades ago I made this beautiful piece of workshop equipment with the full knowledge of how useful it would be some day. It took about a full year of spare time to make the geared version and to produce all of the parts to the high standards needed to have the rolls do all of the things Mr. Thomas said it could do.

The bending roll design allows for a very fine adjustment of roller pressure and the forming roll height while having the gears, the mechanical advantage allows everything to operate as smooth as silk. This is very advantageous with spring steel as it allows one to slowly approach the critical fibre stress in the metal (as the spring steel up to that point will just spring back) where it will take a permanent set (curvature). If you just whack it with a non metallic hammer over a curved bar, you may or may not get the desired result. Not to say that I haven't done it this way in the past.
Attachments
194 Using the G. H. Thomas Workshop Bending Rolls to Form the Leaf Spring Curvature.jpg
195 Another View.jpg
196 Checking the Starting to Form Radius Against the Plywood Template.jpg

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Carrdo
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Re: A Real Dirty Job

Post by Carrdo » Tue Nov 06, 2018 2:40 pm

Subconsciously, when things are going so well, I always start to worry about when Murphy will join the party and he did!

After I formed the required curvature perfectly in two of the top spring leaves (see the first photo), I noticed that the spring steel was starting to scarify and groove the surface of the rear forming roller as it was made from ground but unhardened superior shafting (see the second photo). The square ground ends of the spring steel act like a HSS razor blade shaving and scarifying the surface of the rear roller on every pass and will even dig into it.

Full stop as I am not going to have a piece of spring steel destroy a year's difficult labour in the making of this magnificent piece of workshop equipment.

There are two solutions to this problem - a temporary and a permanent solution.

The temporary solution is to machine up a very thin sacrificial steel sleeve to slide over the rear roller to protect the roller surface from further degradation. The spring steel will chew up the temporary steel sleeve also but it will last long enough to get me through the job. One just has to make a new sleeve every so often.

The permanent solution is, theoretically, to have the forming roller hard nitrided resulting in a glass hard roller surface. Not going to happen as nitriding can distort the part (I made the roller dead straight), I don't trust any local heat treating shop here to do it properly (my experience with them on other jobs) and I couldn't afford the charge as it is a one off.

Alternatively, one can (theoretically) buy, commercially made, extra thin wall (0.032") hardened steel drill bushings of the correct size to just slip over the forming roller (as with the temporary steel sleeve). Problem is they are "specials" and "unobtainium" here in Canada. Better still, they could be made from solid carbide (this exists theoretically also but are custom made only by the largest US corporations). Guess what they would want as a minimum order and how many hundred pieces....

The above just goes to show what a nasty and difficult material hardened blue tempered spring steel is to work with.
Attachments
197 Two Top Leaf Springs Finish Curvature.jpg
198 Bending Roller Surface Scarification and Grooving.jpg

John Hasler
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Re: A Real Dirty Job

Post by John Hasler » Tue Nov 06, 2018 3:37 pm

Can you run the springs through between thin backing plates?

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Re: A Real Dirty Job

Post by Harold_V » Tue Nov 06, 2018 4:47 pm

Carrdo wrote:
Tue Nov 06, 2018 2:40 pm
I don't trust any local heat treating shop here to do it properly (my experience with them on other jobs)
You didn't mention the problem(s) you've experienced with the heat treating shops, but one thing needs to be mentioned, and that is that heating ANY material, regardless of its nature, tends to relax internal stresses. That generally manifests itself in distorted configurations. I make mention because it may not be the fault of the heat treat shops, but the result of working with unknown stresses. That's the thing one should take away from this comment.

I recently machined a worm for the muller I restored to operating condition. I entertained the idea of nitriding, but abandoned the thought due to the amount of heat involved. It should be noted that if the material one hopes to nitride isn't heat treatable, it also doesn't respond to the nitride process, something I was not aware of until I talked to a shop involved in the process.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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Carrdo
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Re: A Real Dirty Job

Post by Carrdo » Tue Nov 06, 2018 7:11 pm

Back in business.

I really didn't need any of this but ... live and learn.
Attachments
199 The Extra Thin Wall Roller Sleeve After Case Hardening.jpg
200 Back in Business.jpg

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Carrdo
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Re: A Real Dirty Job

Post by Carrdo » Wed Nov 07, 2018 9:50 am

There is always a better way which I didn't think of.

Richard suggested using what is known as "Thompson Shafting" for the rear forming roller as a permanent solution. It is readily available here (Canadian Bearings), it has a rock hard (62 Rockwell) surface, it is dead straight, on size and has a bright ground smooth finish. He said that the spring steel ends wouldn't touch this surface.

One would have to use carbide cutting tools to machine the ends of the shafting down for the end bearings but the material is softer further away from the hardened surface.

He used this material exclusively when he rebuilt his CNC bench milling machine.

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