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Post by powderhorn01 on Feb 18, 2011 15:56:58 GMT -5
In the Kozo A-3 book on page 69, I spotted an error. Fig 10-19 shows the milling set/up for the groves for the front bumper. The bumper is rotated 90 deg from what it should be, see fig 10-17. If it is blank stock, no problem, but if you have contoured it and drilled holes, it's a major oops.
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Post by powderhorn01 on Feb 28, 2011 2:20:19 GMT -5
In the Kozo A-3 book, for 1.5" scale on page 19, there are some problems with the measurements for the overall length of the arch bars. Make the bending /drilling jig to what is shown in the book. The actual blank bar length is where the changes are.
1. Tie bar blank length should be 9.75" 2. Lower arch bar blank length should be 11.0" 3. Upper arch bar blank should be 10.0"
If you cut to the measurements in the book, you will come up short after they are bent.
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Post by kvom on Mar 17, 2011 11:09:45 GMT -5
In the A3 book on page 82, the numbering for the main rod bushings 6 and 7 are reversed from drawing 13-2 on page 79.
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Post by kvom on Mar 28, 2011 14:37:46 GMT -5
The plans (pg. 79) show the the main rod bushing flange facing the inside of the rod and towards the spacer and side rod. Given that there is no bushing or spacer on the outside, it would seem that the outer face of the rod would rub against the return crank (pp. 101, 108). Therefore I am wondering if the bushing flange should be on the outside face of the rod providing a bearing surface for the return crank; the spacer bushing then provides a bearing surface between the main and side rods.
That spacer bushing thickness already provides a means of aligning the main rod centerline with the cylinder bore centerline.
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Post by powderhorn01 on Mar 29, 2011 20:42:52 GMT -5
For those of you building the Trucks, in 1.5' / 7.5" gage. BEWARE !!! The measurements for the bolster bars do not double up correctly, it will be short. The correct overall length is 11.0". You will have to adjust the other measurements to fit. Keep the measurement for the side bearings mounting holes the original spacing.
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Post by kvom on Apr 4, 2011 20:42:01 GMT -5
Prior to beginning to machine the cylinder castings I have received, I've drawn the cylinder in 3 views to get and check the dimensions in 1.5 scale. There are a couple I've not found documented:
1) Depth of the steam ports. If the bottoms are supposed to be even with the top of the round portion, as shown in fig 14-3, p. 85, then the depth is .3125", and half that for 3/4 scale.
2) The depth of the steam admission holes needed to meet the angled hole from the steam chest face (section B-B). Drawing measurement shows as .755", half that in 3/4 scale.
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Post by kvom on Apr 24, 2011 13:11:18 GMT -5
Looking at the standard sizes for O-rings for the piston and valve stuffing compared to the piston and valve rods, one sees that for the 3/4" scale the sizes are:
Piston rod: ID = 3/16 nominal, OD= 5/16 Valve rod: ID= 1/8 nominal, OD= 1/4
While the O-ring dimensions are not shown in the book, these values match up well with the ID and OD of the bushings and the bores in the steam chest and rear cylinder covers.
For the 1.5" scale, modifications may be necessary. Doubling the valve spindle diameter (pg. 103) to 1/4, the valve O-ring sizes are ID=1/4, OD=3/8. Using the piston rod diameter of 3/8 (pg. 223), the O-ring dimensions are ID=3/8, OD=1/2. This means that the OD of the bushing and the ID of the bores are less than double that of the 3/4 scale since the difference in ID/OD remains 1/8" for all sizes
In both cases, Kozo specifies the bores as about .008" larger than the OD of the ring, and the bushing as .001-.002 smaller than the bore. Given the same allowances in 1.5" scale, the bore on the steam chest would be .383, and that on the cylinder head would be .508.
It may well be that having the bores larger than the actual O-rings would not matter, but I thought I'd point this out.
One should note that the thickness of these rings is .07" regardless of size. Kozo's longitudinal spacing of 3/32 between the end of the bushings and bottom of the bore leaves 1/32 for expansion of the ring. This applies also to the ring and bushing for the axial water pump.
*** addendum 5/24/2011
Referencing the Parker O-ring handbook wrt the A3 3/4 plans, the size for the valve stem ring (1/8" shaft) is the 2-006. This ring has an ID of .114. Using Kozo's bushing OD of .257 gives a difference of .143. The size of the piston o-ring (3/16" shaft) is the 2-008 with an ID of .176. The bushing difference is .319-.176, or again .143". This constant is due to the fact that the thickness of both rings is .07.
Assuming doubling of the shaft diameters for 1.5" scale, we get:
1) Valve stem = .250", o-ring 2-010 ID=.239, bushing OD=.239+.143 = .382.
2) Piston = .375", o-ring 2-012 ID=.364, bushing O=.364+.143=.507.
Using a piston rod larger than .375 would require a different formula as the next size o-rings are thicker than .07".
If you double the length of the bushings and add the 3/32 allowance, then the bore depths are:
1) Steam chest = 23/32 = .719
2) Rear cylinder head = 25/32 = .781
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Post by kvom on Jul 7, 2011 7:42:48 GMT -5
Re: Kozo A3, pg. 96, fig. 15-17 (Crosshead Pin):
In 1.5 scale, the diameter would be determined by the thread size. The drawing shows a 8-36 thread with the diameter .001 larger than the major diameter of the thread.
The nearest imperial thread at double scale is 5/16-24, so the pin diameter would be ~.314" rather than .329 from doubling the plan diameter. This then modifies the crosshead hole diameter to ~.315 rather than .330 (pg. 94, fig 15-8). Finally, the diameter of the hole in the main rod bushing (pg. 82, fig. 6) would also need to be .315.
If both the crosshead and bushing are to be reamed, the either a 8mm (.315) or O (.316) would be used with appropriate fit for the pin.
Another pin thread size and diameter could be chosen to match a reamer that a builder has on hand, but that decision should be made before drilling the crosshead and bushing.
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Post by kvom on Jul 11, 2011 13:10:45 GMT -5
Kozo A3 pg. 216 Fig. 3-13: shows 12 required 5/16 pins numbered 20 for the brake assembly. However, I can find only 6 of this size in the drawings: 4 for connecting the brake lever links to the brake levers, and 2 for connecting the ends of the brake rod.
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Post by kvom on Jul 12, 2011 9:14:03 GMT -5
Info on brake springs: Kozo A3 pg. 216: McMaster-Carr has springs that match Kozo's specs almost exactly. Return spring (#23) is part number 9433K36 (sold in packs of 3). Compression spring (#22) is part # 9435K3 (pack of 5).
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Post by kvom on Jul 25, 2011 15:29:49 GMT -5
Drawing of the brake shoes (1.5 scale, p. 213, fig. 3-2) shows a radius for the face as 3-3/16, corresponding to 1/16 less than the doubled driver radius (3-1/4). I'd argue that the radii ought to be equal, but in any case the radius would need to be adjusted to the actual driver radius if drivers are machined from commercial castings. In addition, the distance from the face to the mounting hole (shown as 3/4") may need to be adjusted as well in order to fit without rubbing.
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Post by kvom on Jul 28, 2011 7:19:38 GMT -5
Some feedback I received from an experienced builder on a couple of issues I've seen with the 1.5 scale:
1) Getting oil into the axle bearings will be a problem, as any access to them will be difficult when fully assembled. There is a good case to be made for using sealed roller/needle bearings rather than the bronze split bearings Kozo designed. My alternative will be to keep the bronze bearings but drill holes in the axles with Gits oilers to feed oil to the bearings.
2) The retaining side rod pins (p. 77, fig 12-16) for the front crank pins are going to be impractical in large scale, as there is no access to the e-clip once assembled. Removing the side rods would then require removal of the brakes, detaching the axle pump, and lowering both axles from the frame. The recommended solution is to thread the crank pin and attach a thin retainer disc to the end of the pin with a flathead screw.
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Post by kvom on Aug 2, 2011 13:11:59 GMT -5
I drew the tie plate for the 1.5" scale using the following assumptions: 1) X dimensions outside the frame are 2X 2) Y dimension are all 2X 3) The radius is computed used a 3 point fit In 3/4 scale the plate is 1" wider than the outside frame. I have attached my drawing as a PDF in case it benefits anyone else, or if any errors can be seen. Attachments:
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Post by kvom on Sept 16, 2011 11:54:55 GMT -5
Minor typo: p. 113, fig. 18-12. You need 2 of these collars, not one.
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Post by kvom on Sept 17, 2011 18:30:10 GMT -5
A3 in 1.5" scale: there appears to be a mismatch in the hole locations needed for mounting the running boards. My calculations are as follows.
1) On the frame drawing on p. 206, there are no dimensions given for the support plate mounting holes on the foot plate, plus the foot plate width given is twice the 3/4 scale dimension. Therefore the location of the inner mounting hole will be 4.4375" from the centerline, calculated from p. 63.
2) The inner running board mounting hole in the support plate has the same displacement, as shown on p. 112.
3) If you accept that the tieplate dimensions I derive in the drawing attached to post#87 are correct, then the yoke mounting holes are 3.969" from the centerline. Then from the yoke drawing on p. 100, the inner mounting hole is .625" from the tieplate mounting holes. This gives the inner running board hole on the yoke as 4.594" from the centerline.
The difference of 4.594-4.4375 is .1565 or 5/32" further outboard than the corresponding hole in the support plate.
I would recommend that 1.5 scale builders measure the distance between the mounting holes to verify any differences on their build.
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