HP Forums

Full Version: HP 46/81 idler gear
You're currently viewing a stripped down version of our content. View the full version with proper formatting.
Was at the local library and they have the Innovations Studio in town. Laser cutter, CNC router, 3D printer, etc. Its somewhat "canned" so making your own custom stuff has difficulties. At least with the utilities they provide.

Never saw a 3D printer in action and was surprised with how fine a "thread" it can extrude.

Which made me wonder, with all the expertise here or elsewhere has anyone tried to 3D print the idler gear for the 46/81 printers? (you know the gear that always breaks) When its done some whittling or filing might be necessary, but "cleanup" for the produced item seemed easy. (they were making a cookie cutter)

Over my head. Anyone have thoughts on that?
Working on a gear for the HP 97 right now and getting close.
Dear Duane,

It works! Ya, I am excited as I have been at this for awhile.

I do not see why this would not work for a 41/81 of which I am not familiar.

Will post to my thread in the general section as soon as I test some more.

Regards, Rick
Hi Rick, Hi Duane

congratulations for your HP97 gear :-).

I tried same on HP46/81 gear (mentioned by Duane), some years ago. Without 3D printer at my side and missing CAD skills I asked a colleague, but she had to admit that her software tools are not able to create a compound gear.

So I repaired around 5 HP-46 and HP-81 machines and gave away same number of my "glued" gears over last 4 years. At least my machines are still running. Costs are below 10 $/€ per item.

As you mentioned and proved, it is not impossible to create a more professional 3D printed solution. Drawback: a lot of time and trials.

Here is a possible starting point for working gear parameters.

Best regards,

Dear Werner,

Nice gear and great solution.

My biggest problem was lack of knowledge.

Forty seven years ago I studied gears. Found my old schoolbook and was shocked at what I did not remember.

About thirty five years ago I taught myself cad with Generic Cadd on a dos machine. When I could afford Autocad, I also hired some talented folks much better than me and hardly ever touched it afterwards.

OpenSCAD is different. Open source, free, and very nice.

I have not yet figured out how to insert photos in a post so will attach some files.

Just occurred to me that I have not yet printed on paper. Might be too happy too soon.

Regards, Rick
Hello Rick,

thank you very much for sharing your results :-)

I am pretty sure that I will use your solution, either by feeding my own 3D printer or by ordering via Shapeways & Co.

At the moment I am doing stocktaking of all my calculator stuff for the first time. I know there have to be some HP-9x machines around but I have not found them, yet...

Best regards,

Dear Werner and Duane,

Whew. My gear prints on paper just fine.

I have ordered some HP 97 gears from Shapeways and should have them in about a month. For all of the plastic materials I had to check a box saying print anyway. This suggests that their algorithm thinks I might not be satisfied with their quality.

The tips of my gears are slightly rounded and stubby. I kept try things until something occurred to me. My printer has a 0.4mm nozzle. It is impossible to print any detail smaller than this. Because the hot material is smashed and dragged, 1mm or 2mm is probable more realistic. Did not seem to matter on this gear.

I also order 1 steel gear just to see what it is like.

Wow. The hours I've spent in the shop machining prototypes.

As an exercise I have drawn and printed an Hp 46/81 gear. Easy to do now. Not sure if dimensions are correct.

Attached is the OpenSCAD file with some screenshots. The stl file can be uploaded to Shapeways for an instant quote.

They will print with versatile plastic for $5.00 + $10.15 handling or in platinum for $4,873.69. <grin>

Regards, Rick
Fantastic! Well done! I love OpenSCAD, too! I will definitely be trying this!

Cheers -

Hi Rick,

absolutely cool stuff. Could take a little time, but I will definitely try your solution :-)

I received HP 97 printer gears from Shapeways on Saturday.

From order to delivery was 11 days. Not bad.

No modifications were made except to open the hole with a 3/32" drill.

Checked them by fitting to a printer and feeling by hand for binding or slop.

Some photos are attached.

HP Gear, Light brown

We all know what this is like.

My Gear, PLA, Yellow

Slightly rounded teeth, nice fit. Tested well.

Shapeways, Versatile Plastic, White

Slightly rounded teeth, nice fit.

Shapeways, Fine Detail, Clear

Well formed teeth, nice fit, almost perfect.
Description says brittle but I think they mean in relation to other choices as
it drilled easily and I threw onto my tile floor with no damage.

Shapeways, Steel, Silver

Very rounded teeth, oversize and would not fit, magnetic, very hard to drill
because of the added bronze. Did not plan to use anyway, but so many possibilities.

I plan to use my PLA gears that were tested for 40,000 print cycles but the
Shapeways gear from fine detail plastic is really nice and I think the best 3D print.

Regards, Rick


Not sure my post has a point; you've probably know most info in it. But do you recall in your past after asking a person questions they stop and look at you for a moment? Much to your suspicion of their pondering "Do you really want to be punished?" was true. Woe to the person who does not ponder whom can communicate succinctly. Fortunately, you never asked me a question so... the punishment, err, my elaboration will be minimal. (and there is a suggestion at the end)

Used Sadsilence's solution myself; worked well. There have been numerous posts on the 46/81 printer. Believe many revolved around alignment the printer itself as opposed to gear specifications. If you're curious about the printer you might try:Epson 102
to see pictures with the covers off.

As you already know, the gear is a speed reduction idler combination gear of 17/68 teeth Mod 0.4. From my measurements with an old mechanical slide micrometer:
- small gear 7.5mm diameter, 3.9-4mm "tall" (thick)
= as odd # of teeth, one side of micrometer is setting on the corners of 2 teeth and other jaw is on the point of a single tooth
= if I understand correct [(#teeth + 2)*module] produces a very good value for outer gear diameter. 19*.4 = 7.6mm
= calculated pressure angle 27-28 degrees (thrust angle?) (described later)
- large gear 27.8mm diameter, 2.9-3mm thick
= micrometer mispositioned: each jaw was sitting on corners of 2 adjacent teeth. should have been tip to tip of opposite teeth
= (68+2)*.4= 28mm
= calculated pressure angle 18-20 degrees (described later)
- the gears have a 3mm bore. The bridge shaft measured 2.9mm. "Bridge" is how HP/Seiki printer documentation refer to the removable plate and shaft supporting the gear.
- overall gear thickness 7mm
** it should be noted I have no background using a micrometer. The first time using one was to measure this gear. The micrometer supposedly has a +/- accuracy of 0.1mm. Who knows what my accuracy is.

For your reference the printer in a 46 & 81 is a Shinshu Seiki EP-102. You may find various manufacturer names as several companies (owned by various family relatives) evolved names & formed subdivisions. Basically Suwa Seikosa -> Shinshu Seiki -> (some products+printers) -> Seiko; Shinshu Seiki -> (printers especially) Epson. The part number for the gear (hoping someone will find a stash somewhere):
Shinshu Seiki: B-2-11 "Idler Gear Wheel"
HP: 1535-3243
Seiko: 1240120

The "Gear Comparison" jpeg in the "HP 97 Printer Gear RPZ rev2" zip shows key geometry consistent with the 17 & 68 combo gear:
- rounded trough bottom (essentially or is circular)
- side extends up at an angle
- approx. top 1/2 of tooth angle changes again to match pressure/thrust angle
- end of the tooth is blunt (snub nose--flat)

I was curious what material PLA (yellow gear) you refer to is. Along with what material comprises the Shapeways fine detail & clear gears. Are they nylon, delrin, polyacetal? My interest centers around gear's relative hardness.

Wondering, as my opinion of the 46/81 combo idler (spur?) gear and the 97 printer idler gear is they were intentionally made of "sacrificial" material. Unfortunately, the material falls apart also. Sacrificial meaning made of a softer material as to incur most of the gear train wear. Hence, lessening wear on the gears connected to. In the EP-102 printer its obvious replacing the motor gear or drum gear would be much more difficult/consequential than replacing the combo idler gear. The fact the combo idler gear is an a separate removable plate ("bridge") underscores that design philosophy, in my opinion.

Is the issue of a softer sacrificial gear actually that important? Likely debatable . But I would not use a metal gear unless no other alternatives exist. Further, I'm more a hobbiest than anything, so my minimal use wouldn't underscore any vailidty to the concern irrespective.

However, consider automotive comparisons; granted high-force and extended duty cycles. Car people know you replace geared components in pairs. For example, you don't replace metal timing chains without a full timing kit (gears it runs on). Likewise you move the gear from an old replaced distributor to the new one. If the new distributor gear is used, replace the cam shaft gear also. People with rear-wheel drive cars likely have seen the differential gears. You'll notice a wear "pattern" between gears. The pattern is random & unique with each gear set. This is why you replace gears in pairs, particularly in large force and duty cycle situations.

Imagine your hands being two gears originally with nice and squarely aligned teeth. Now, years later, make one hand cup shaped and the other a fist. Put them together and pretend they are worn gears. Although worn, maybe with vibration, etc. the fist and cup fully seat. To make the point, replace the fist with a square of cardboard. Slide the cardboard along the cup shape. Contact between the two will be only in a few points. Small contact surface creates massive wear at the same points. Hence, you replace gears in pairs. Practical for cars, but not really for these printers in my opinion. The EP-102 motor & drum gears would be a tedious issue.

What's the point? I would like to know the relative softness between the gears at Shapeways and PLA (whatever it is). Personally I would like to share some info. I have minimal ways to examine the original gears and newer replacements--the 17 & 68 individual gears you can use to create a combo gear.

I made images on a flatbed scanner of the remnant pieces of the original broken gear. (gee 3D doesn't work well on a flatbed scanner) Results weren't that bad. Picked up the scanner (combo printer, copier, scanner, etc.) at a yard sale for about $10. Scanned the large and small gears at 800DPI. Cut & pasted the gear only from the 8-1/2x11 inch image into a jpeg of its own. Portrait printed the gear on letter sized paper. So ended up with a 10 in wide gear. Unfortunately the only ink I had came with this 10+ year old device, only printed pink & ran out quick; ended up with crappy printouts. However, using a ruler and doing some trig am pretty sure of the following:
- the thrust angle of the large gear is somewhere between 18-20 degrees
- the angle for the small gear appears more like 26-30 degrees (probably 28); the small gear was tedious since the ink ran out
Off the shelf gears generally have a 20 degree angle.

Now I know why I keep a bunch of little boxes/vials full of broken chunks of all sorts of stuff that comes out of equipment. You never know when its useful!

If you are interested (and will return my gear chunks) I would be happy to send them for your examination (my expense). Should you be interested in comparison with your gear. Magnifying glass examination shows the thrust angle between the 17 & 68 tooth gears are different (or look that way). I don't want anything in return (other than returned parts unmodified) but would appreciate microscope images of my gear pieces. A flatbed scanner doesn't work well. Naturally the hope is you would verify and modify, if needed, your 3D printer definitions so we all can obtain gears from Shapeways. Or that's how I took your posts, you created 3D definitions and were allowing the rest of us to purchaes parts from Shapeways (or you?).

I understand you have a life, etc., so I don't want my gear parts returned in a week. A few months is fine. (a year would annoy me). Maybe you're not interested, but took it as your familiarity with the gear is relatively limited. I have the full 68 tooth gear and 17 tooth gear (separated), but about 1/3 of the teeth on the small gear are chipped.

Please let me know your interest and we can make shipping arrangements. Will include my horrid printouts. For you reference on how I came up with the thrust angles. Actually for my reference, to see whether I have a clue. Don't know crap about gears other than once upon a time owning 70's era cars. And what I've read on the Internet, as to have a clue to talk about it.

Please let me know.

I mean:

Hi Rick!
Hello Duane,

Thought I posted a response to your post a long long time ago. Oh well. Sorry.

I am a hobbyist who enjoys repairing and using older HP calculators. Part of this is that I could not afford them years ago when they were introduced. I have no desire to sell parts or start a repair service. Just wanna have fun. I buy way too much on an auction site (must stop) and have yet to sell anything. The purpose of my posts was only to assist anyone else attempting to print 3d printer gears. Feel free to use or modify any information provided.

Due to the small forces and low usage, I don’t think wear is really much of an issue. I have tested my HP 97 gear for 40,000 cycles and can see no visible change. That’s over 6 rolls of 85’ paper. The usual idler gear replacement is made of aluminum driven by the steel pinion and driving the large plastic gear. Aluminum is very abrasive but no one has ever reported a wear problem.

PLA is short for Polylactic Acid and is often used for 3D printing and many manufactured items. This is the material I used for my gears. The tips of my gears are a little bit blunt due to the limitations of my printer but did not seem to matter in my testing. Sometimes this is done on purpose in gear design and is termed clearance.

Fine Detail Plastic from Shapeways is described as a resin-based acrylic material. It is not recommended for functional functional parts due to its brittleness. Brittleness is such a relative term. Cast iron is brittle but often used for gearing. Shapeways printed a really nice detailed accurate part with this material.

I don’t think any of the gears were meant to be sacrificial. My guess is that they picked a material for wear and sound. I’m sure they did a bunch of testing but there is no substitute for age. Thinking of the card reader gummy wheel.

I only printed the 46/81 gear as an exercise as I do not have one but you never know. Never thought I would have a 97.

If you would like some to test or use I would be happy to mail you some. Let me know.

Regards, Rick
(09-05-2022 01:35 AM)RPZ Wrote: [ -> ]I don’t think any of the gears were meant to be sacrificial. My guess is that they picked a material for wear and sound. I’m sure they did a bunch of testing but there is no substitute for age. Thinking of the card reader gummy wheel.

The only reason I can think of for sacrificial use is that if the printer driver fails, the carriage can slam against the side of the printer casing and damage the mechanicals and/or the motor. Once a line is printed, the software only waits in a permanent testing loop for the carriage to home, but it does not have any timeout code if the carriage fails to return, so the motor will keep pushing the carriage into the casing. I have no idea if the PIK chip caters for this situation internally. If the motor timing components on the printer driver circuit board fail, this could occur but seems a rare event.



I'm glad you made your posts. My using sacrificial is probably not the best. I, indeed, meant sacrificial in terms of wear. i.e. obviously the gear on the print drum and drive gear on the motor shaft are way more difficult to replace than the idler gear. Hence, make the easiest gear to replace take the brunt of the wear.

Maybe metal isn't of any significance in terms of wear. If I knew the softness of the drum gear I'd probably want an idler gear from material known to be softer. But we all want things, especially when the less important it is the more you want it. ..... think they call that a "habit".... a calculator habit. :/


Yes, if you have a printed PLA 46/81 gear or two I could try, I'd be happy to take them. If you're interested let me know & I'll PM you my address.

I don't sell things, but have traded things. Now that you have a 97 would you be interested in some 97 blank cards in return?
Hello Duane,

Good to hear from you.

These are the measurements I picked up from the forum to print gears.

I did not print the hub on the 97 gear thinking that it would be easier to see wear and if there was some I could flip it around and use it again. They seem to be working well. Once designed it’s just a matter of pushing a button and using about 3 cents worth of material.

I was a little bit unsure following the 46/81 thread as to the thickness. Perhaps you could verify as you have one that works.

HP 97 Gear Parameters

30 teeth
80 pitch = pitch diameter
20 = pressure angle
0.100” = gear face thickness
0.078” = hub thickness
0.250” = hub diameter
0.125” = bore

HP 46/81 Large Gear Parameters

68 = teeth
0.4 = module
20 = pressure angle
1.256mm = circular pitch = mm per tooth
2.500mm = gear face width
3.200mm = bore

HP 46/81 Small Gear Parameters

17 = teeth
0.400 = module
20 = pressure angle
1.256mm = circular pitch = mm per tooth
2.500mm = gear face width
3.200mm = bore

I got lucky a while back and found a whole box of new cards at a great price and am in good shape. Thanks. I am just curious if a printed gear will work and if you are willing to test that would be great.

Along those lines, I have spent a lot of time trying to clean and reuse cards. The ones marked with sharpie did not clean with alcohol or any other solvent I had on hand. Even tried spray painting and sanding. Sorta worked but always a bit thicker and decided not to risk damage to my rebuilt card readers.

Pencil should be no problem right? None of my erasers worked. Finally bought a Tombow Sand Eraser 512A and it works well. Very fine abrasive and if I am careful, removes pencil without rubbing thru to the black underneath.

If you can verify the gear thickness, pm me an address and I will try to mail some gears in the next week or two.

Regards, Rick
Reviewed various posts in the archive. Sure I didn't see all of them.

You are correct the gear is modulo 0.4 and 68/17 teeth. Don't know about the pressure angle, but any gears you order (I've fabricated several from individual gears) always seem to be 20 degrees. Circular pitch means nothing to me. Know nothing from gears, but I take it module and teeth count defines all kinds of stuff, like total outside circular diameter, some diameter near bottom of teeth (reference) (circular pitch?), circular pitch, diametrical pitch and a whole bunch of terms I have absolutely no understanding of.

Put used gears under a USB microscope I have, angles of the thrust surface vary greatly from 23-28 degrees. I assume that's wear, as the edges were always rounded. I don't know beans about gears, but any Google research I've done on all kinds of old 70's products, 20 degree thrust angles seems to be a standard.

You know, it never dawned on me until now why I haven't tried viewing gears from devices I know that have had little use. i.e. a Canon unit I purchased new and other stuff. Guess I'm dumb.

The teeth face width and hub width are the same. The overall thickness of the gear is 7mm. Thickness of the 68 teeth gear is 3mm. As you can guess the thickness of the 17 tooth gear extends 4mm from the side of the 68 toother.

The bore is 3.0mm. I've fabricated a number of gears, all were 3.0mm; fit well, no wobble and no binding. 3mm corresponds with posts/notes I've had with other users. There was a 3.0mm bore fluted brass ferrule which took a 3.2 bore gear. But that ferrule doesn't seem to be available anymore. It was quite handy.
Glad I asked. Not sure where I picked up some of my numbers.

HP 97 Gear Parameters

30 teeth
80 pitch = pitch diameter
20 = pressure angle
0.100” = gear face thickness
0.078” = hub thickness
0.250” = hub diameter
0.125” = bore

HP 46/81 Large Gear Parameters

68 = teeth
0.4 = module
20 = pressure angle
1.256mm = circular pitch = mm per tooth
3.000mm = gear face width <—corrected
3.000mm = bore <—corrected

HP 46/81 Small Gear Parameters

17 = teeth
0.400 = module
20 = pressure angle
1.256mm = circular pitch = mm per tooth
4.000mm = gear face width <—corrected
3.000mm = bore <—corrected
Reference URL's