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17th Feb 2017, 06:49 PM #1Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
- Posts
- 930
Harrison M250 Change Gear Test Spline
A test splined bush made to test a milling approach.
1. Original Harrison 22T gear.
2. Gear with a piece of CI material recovered from the local TAFE scrap bin.
3. Cutting material down to machinable size, can make two bushes.
4. Facing material.
5. Drilled 8 mm to fit mandrel.
6. Material on mandrel with OD made cylindrical.
7. Double bush in collet bored to fit spline ID.
In foreground is the test mandrel for size and a timber lapping bar.
8. Double bush Loctited on mandrel, finished to OD size, then separated into two bushes, each on size for OD, ID and thickness.
9. Bush on rotary table with 5 mm slot drill gashing 6 slots.
10. 4 mm end mill finishing side of slots.
11. Finished sample splined bush.
12. Bush fitted to gear shaft on lathe.
All in all, a complex task that came off.
The fit is acceptable, but a little loose.
Not sure I would recommend this method, too many ways for it to go wrong.
I plan to make a 63T gear wheel that will be Loctited to this bush.
The next bush will be done with a 1/4 " linear broach.
John
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3rd Mar 2017, 11:14 PM #2Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
- Posts
- 930
Well, some progress, 2 steps forward and 1 step back.
A mate decided that he would invite me over for a working day to make a broach bush and then broach out two blanks.
Two blanks so that there is always at least two teeth of the broach in the cut.
We made the broach bush.
First a 9 mm slot drill for the prime broach slot, then some +/- side shift to get the 3/8" = 9.64 mm dimension for the 1/4" standard linear broach width.
Then a 1/4 " slot drill for two shallow slots at 60 degrees and 240 degrees to take an alignment key for the multiple broach presses, some from the opposite side.
Two blanks were made from some beautiful 116 mm extruded CI bar, one at 97.5 mm for the 63T gear and one at maximum diameter for future.
The two blanks were then broached in the standard way, indexed and repeated as appropriate, heading towards the desired 6-way spline.
The disaster !
It became obvious that the broach bush +60 and +240 degree slots were off, by a considerable margin, see attached photo.
A re-cap revealed the problem.
The last offset of the 9 mm slot drill to achieve the 9.64 mm width had been left on the Y-axis when the dividing head was rotated for the 1/4" slots, so both were off by that amount.
At home, licking my wounds, I decided to use my milled bush to make the 63T gear and bored out the gear blank to suit a Loctite fit of my milled centre bush, see photo.
Tomorrow, I will review the situation to see if the remaining blank can be rescued.
I am thinking that most lathe change gears get by perfectly well with one key, so I can just mill out the incorrect slots and make do with the remaining slots.
The broach bush is probably beyond recovery.
It appears to me that we nearly got there, so a broached solution for the 6-way spline looks entirely achievable.
For a 1-off, the milling approach is probably the easiest way.
Gear Blanks Broached 1 Compr.JPG
John
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4th Mar 2017, 02:15 AM #3Senior Member
- Join Date
- Jan 2012
- Location
- Hinchinbrook
- Posts
- 112
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4th Mar 2017, 08:55 AM #4
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4th Mar 2017, 08:58 AM #5Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
- Posts
- 930
Phil,
My understanding is that this CI is a ductile grade continuously cast, fed through a die and the leading end pulled away from the die.
The bar is closely circular with visible striations and no sign of any marks that would be left by rollers or a mould.
Not sure if this is done vertically or horizontally, but I suspect vertically initially, with a curved path of rollers leading away from the casting station to the horizontal.
Everyone I know, including instructors at TAFE, refer to this product as 'extruded'.
John.
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9th Mar 2017, 09:29 PM #6Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
- Posts
- 930
Success.
We made a new linear broach bush and used it to make two blanks.
Fit is a little tight, one goes onto the lathe QCGB input shaft with a tap, but not onto the banjo shaft.
The other refuses to engage either shaft, just.
I am confident a little fettling will fix both blanks.
The broached approach looks entirely practicable.
The plan is to purchase the required M1.5 cutter for 63T.
I now have three splined blanks and one blank with an incorrect spline (that may be usable).
Gear Blanks Broached 2 compr.JPG
John
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9th Mar 2017, 10:29 PM #7Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
- Posts
- 930
The fettling is not so easy, especially after a couple of glasses of a nice shiraz.
The ID on the blanks is loose, as tested by my mandrel.
The mandrel is a tight fit in the Harrison gear and slightly loose in ours.
Our slot depths are much greater than the Harrison.
A piece of 1/4" HSS is a firm fit in all the slots of the gears we made, and just refuses to enter the slots of the Harrison gear (so it is outside the tolerance on the manufacturing drawing).
The only things left are slight rotational errors - but where is very hard to say.
Tomorrow I will try to develop a rotation measure to sort out which slots are out of place.
An easy start is to take the banjo shaft off the lathe and offer the blank up over a bright light at the bench - that may show up the slot flank(s) causing the problem.
John.
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9th Mar 2017, 10:29 PM #8Pink 10EE owner
- Join Date
- Aug 2008
- Location
- near Rockhampton
- Posts
- 6,216
Could you partly mill the slots out first to take some pressure off the broach? Broaches being expensive items and all.
Gold, the colour of choice for the discerning person.
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10th Mar 2017, 08:50 AM #9Mechanical Butcher
- Join Date
- Oct 2004
- Location
- Southern Highlands NSW
- Posts
- 1,894
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10th Mar 2017, 09:43 AM #10Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
- Posts
- 930
With the banjo shaft off the lathe and a bright light, the fit issue is revealed.
It is not angular errors so much as the shape of the teeth in the blank.
The Harrison gear has a much more rounded shape to the spline tips.
The 1/4" HSS blank enters through the the tips but does not enter to the bottom of the slots.
The fit of our blanks is very close and only needs a touch with the file to get the banjo shaft to start easing into the blank - but it is very easy to overdo the metal removal.
I think I will rig up a filing guide to ensure the file is always perpendicular to the gear blank, with a bright light to monitor filing progress.
This will take a few days away because of other commitments.
The need for such fettling does mean that the broaching approach for gears is a bit more difficult than hoped.
Bearable if making splines for a few gears for personal use, but not practicable to make a number of gears for others.
The factory may have used a single broach shaped to do all the spline teeth in one pass, specially shaped for their needs.
John.
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10th Mar 2017, 12:37 PM #11Golden Member
- Join Date
- Oct 2008
- Location
- Cairns, Q
- Posts
- 666
John,
Did you check whether the commercially produced 1"x 6 spline hubs will fit the Harrison splines? This would be an easy way to go if they are suitable. They are 1.75" long, so one bush would provide more than one gear centre. The o/d is 2". They are supplied soft, so can be machined to suite the sprocket or gear. They can be hardened if required. Welding instructions seem straightforward. They also make a thin walled coupling 2.75" long and 1 3/8" diameter with the same spline, but warn that welding on these requires care.
They are listed here:
http://www.hydairdrives.com.au/image...ansmission.pdf
The hubs are on page 6, part number94/50005, and the couplings on page 7, part number 94/60005
Frank.
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10th Mar 2017, 07:37 PM #12Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
- Posts
- 930
Frank,
I identified splined hubs early on as possible candidates and talked to one company in regional NSW about them, requesting some detailed data to identify just what standards the spline was made to.
I received nothing by return.
Further investigations seem to indicate that all currently available splined hubs are made with an involute shape, not the parallel sides required by the old British Standard called up for the Harrison gears.
Definitely, the SAE standard is involute, and the common ANSI standard is involute.
Where a spline is listed as "IMP/ANSI", I take it to be the involute.
Current DIN standards I understand are also involute.
What is interesting is that copies of SAE, ANSI and DIN standards are legally available for about $50 or so.
The only copies of the BS standard that I could find were about $325.
I think this reflects the fact that the BS standard is now regarded as obsolete.
If someone can come up with a component that is specifically listed as made to the old BS standard, I would be delighted.
John
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16th Mar 2017, 11:45 AM #13Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
- Posts
- 930
It is a very wet morning in Sydney, ideal for sitting at bench with a bright light, lathe shaft, texta pen, fine file, filing alignment block and the recalcitrant blanks.
The small blank was done first using the texta and no file guide with attention to the tooth shape, as mentioned before.
The final fit is Ok, without being exceptional, a re-think was obviously necessary.
Before starting the large blank the shaft and both sides of the blank were identified with centrepops and a filing block rigged up.
The fit was very closely checked, some flanks were showing light leakage, others not.
A systematic approach tracking which blank flanks were close in each of the 12 possible positions, quickly showed that the lathe shaft was essentially symmetrical and that one flank appeared to be the worst offender.
This flank was then filed square with the guide, and a new check made.
This cycle was repeated a number of times as flanks sequentially became the target.
Final fit was achieved in about 30 minutes, a good fit that is very pleasing.
The fettling on the large blank was quick and not difficult, so the broaching method can be regarded as perfectly acceptable.
Gear Blanks Fettled comp.JPG
John
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