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Nylon milling machine gears

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  • drawfiler
    replied
    The plastic gears in this type of machine failing is quite common, there seems to be a design fault. I have hobbed pairs of gears in steel as replacements, these have been successful and long lasting.
    if anyone would like a set for their machine, please make contact

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  • Doozer
    replied
    Originally posted by PStechPaul View Post
    It should be possible to add a spring to the end of that handle such that it will hold tension on the gears in both positions.
    Putting a spring on the shift handle (I have seen bungie cords used)
    is a terrible idea. It will wear out the shift fork. Seen it many times.
    I do however question why the spring loaded ball detent is not holding
    the shift knob in position. Perhaps the ball compression spring is too
    weak or the ball has worn a path between the detent positions and
    the end holes that detent the ball are not deep enough. The detent
    mechanism is likely under the shift knob.

    -Doozer

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  • loose nut
    replied
    Originally posted by Video Man View Post
    On the issue of $70 gears, if you can create an .stl file of the gear from your cad program, you can have them commercially printed very inexpensively. There are any number of vendors, I am using Jawstec for glass-filled nylon gears for a project I'm working on and the printed parts are very affordable. (No personal connection to the vendor.) I'm using FreeCad because, well, it's free, and it has an excellent gear production module.
    I can print you a gear like that out of PLA or PLA+ if you want to give it a try. They work OK as change gears.

    I would just need the dims.

    Leave a comment:


  • Willy
    replied
    Originally posted by aostling View Post

    Not only can I imagine such methods, I can remember mine. After 200,000 miles my 1982 Stanza would always pop out of 5th gear. I fashioned a giant rubber band from a bicycle innertube to keep it in place!
    Yes but that wasn't due to the mainshaft and countershaft being forced apart due to radial thrust loads trying to separate the two.

    Your issue likely manifested itself when under load in 5th gear, fine when cruising in 5th, but jumping out when under load?

    We have to remember that the gears in most automotive transmissions are helical and are subject to axial thrust forces as well as radial thrust.
    One issue that would cause your problem could have been improperly adjusted shift linkage, but the source of the majority of the problems like this stem from worn synchronizers,especially when when one takes into account the mileage of the vehicle in question.

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  • aostling
    replied
    Originally posted by Willy View Post

    . . . Can you imagine requiring such methods on a manual transmission in a car to keep the counter-shaft and the main-shaft in engagement under load?
    Not only can I imagine such methods, I can remember mine. After 200,000 miles my 1982 Stanza would always pop out of 5th gear. I fashioned a giant rubber band from a bicycle innertube to keep it in place!

    Leave a comment:


  • strokersix
    replied
    Perhaps a converted metallic gear design to molded nylon (acetal?). Often less than satisfactory if simply change the material. Could be a little more molding shrink than anticipated. Now there is excessive backlash or lack of mesh engagement in addition to a lower strength gear. Just a guess. I have no knowledge of the specific application.

    I am a huge fan of nylon gearing. But it has to be designed that way from the start for best results. Conversions can be problematic. Lower strength material, loses strength and stiffness at warm operating temperature, sensitive to moisture and contamination. But if you stay within limitations nylon gears are excellent.

    Leave a comment:


  • Cuttings
    replied
    I just had a look around but could not find the old shaft. After looking at the parts exploded view on page 13 of the manual my memory is a little clearer. I believe I made a new #290 shaft so I could slightly change the position of the 292 lever which operates the 293 shift fork and lift the gear enough in the low range to completely engage it. Once in the correct position I drilled new dimples in the shaft for the 286 & 291 set screws to hold it there. I have had no trouble since.
    My old memory just kicked in again. The 282 set screw in the 285 high low shift knob can be tightened up to put more tension on the 283 detent spring help to better hold it in position.
    Last edited by Cuttings; 01-09-2022, 01:31 PM.

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  • J Tiers
    replied
    Originally posted by DrMike View Post

    Perhaps this failure is an issue with gear engagement, in which case one would expect it to occur whenever the gear train is placed into the low speed range and is stressed, and not just with this one particular operation. That possibility, however, is directly contrary to what was reported, to wit

    "This milling machine does everything I want, except drill 1" holes in aluminum. I don't do that very often, but when I do, it's mostly ornamental holes thru flywheel webs. And this is the point where my mill lets me down."
    he's going to get better cutters, but that statement is not in contradiction about the problem...... The ENGAGEMENT problem only occurs when drilling large holes.... and elsewhere, as I quoted, he says it works fine unless it pops out of engagement.

    So the engagement issue causes the damage (seems reasonable) and the engagement problem os caused by drilling large holes.

    Also read statement by Cuttings (Larry) who has the same mill: "Now if my memory is correct on this and it has been quite a while, I believe I made a new shaft to fit in there because the detent was not allowing the gears to be fully engaged in that low speed range. I probably still have the original part laying around if I dig a bit. I may have made a drawing for the new part"

    That seems to be confirmation that engagement can be an issue with that mill.

    Leave a comment:


  • Cuttings
    replied
    I have the exact same mill and have not yet had a problem with that gear failing. I do flip the head over, and take the inspection plate off the back and make sure there is plenty of grease on those gears probably a couple of times a year. I found that the original grease easily got throw of the gears so I found a different grease with more adhesive qualities that clings to the gears better. Now if my memory is correct on this and it has been quite a while, I believe I made a new shaft to fit in there because the detent was not allowing the gears to be fully engaged in that low speed range. I probably still have the original part laying around if I dig a bit. I may have made a drawing for the new part

    Leave a comment:


  • brian Rupnow
    replied
    All right!!! You fellows have convinced me. Time to make a raid on the Rupnow Fortune and buy Three annular cutters, a 1", a 15/16" and a 7/8". These things come with a 3/4" shank, and I don't have any R8 collets that are big enough, so I will buy 3 dedicated R8 collets which will take a tool with a 3/4" shank. I will still go ahead and fabricate the aluminum arm which will prevent the mill from jumping out of gear when in low range under heavy load. Thank you for your help.---Brian

    Leave a comment:


  • DrMike
    replied
    Originally posted by J Tiers View Post
    But the issue seems to be that the thing partly drops out of full engagement, putting the full stress on only part of a weak plastic gear. There is no suggestion that it breaks "reliably" as soon as the drill gets to full diameter, based on the description of the problem, and the picture posted.
    Perhaps this failure is an issue with gear engagement, in which case one would expect it to occur whenever the gear train is placed into the low speed range and is stressed, and not just with this one particular operation. That possibility, however, is directly contrary to what was reported, to wit

    "This milling machine does everything I want, except drill 1" holes in aluminum. I don't do that very often, but when I do, it's mostly ornamental holes thru flywheel webs. And this is the point where my mill lets me down."

    Leave a comment:


  • J Tiers
    replied
    Originally posted by DrMike View Post
    I must be missing something here.

    The operator of this benchtop mill reports that it works fine except when he occasionally drills 1" holes in aluminum. When he does this, he strips the expensive and hard-to-replace nylon gears in the transmission. The first indication that the gears are failing is that the transmission won't stay in the low-speed position.

    And the suggested "fix" is to mechanically force the transmission to stay in the low-speed configuration, and increase the damage on the gears???

    How is the solution to this problem not "stop drilling 1" holes in aluminum"?...........................
    It COULD be that "solution".....

    But the issue seems to be that the thing partly drops out of full engagement, putting the full stress on only part of a weak plastic gear. There is no suggestion that it breaks "reliably" as soon as the drill gets to full diameter, based on the description of the problem, and the picture posted.

    Nothing wrong with using a cutter that takes less force to drill. That's entirely reasonable.

    But from the info presented so far, it seems that the problem is more with the mechanism of engagement, and not so much with the strength of the gear. The "operator" is quite familiar with mechanical things, which he actually designs as a business. His comment is:

    "When it first decides to eat that gear, it jumps out of gear into neutral. If you can spare a hand to hold it in gear, it works just fine, but sometimes I run out of hands to do that. It doesn't take much force to hold it in gear, and I'm sure that if it was held firmly in gear so that it couldn't jump out, then it wouldn't wreck the gear."

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  • brian Rupnow
    replied
    This is the shape of the nylon gear I currently have. The tooth form is an approximation
    The gears are measured with a Vernier caliper.

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  • brian Rupnow
    replied
    I have never seen an article or a "how to" on replacing the gear drive with a belt drive on my particular machine. If anyone has that, I would certainly appreciate a link or referral to it.--Brian

    Leave a comment:


  • DrMike
    replied
    I must be missing something here.

    The operator of this benchtop mill reports that it works fine except when he occasionally drills 1" holes in aluminum. When he does this, he strips the expensive and hard-to-replace nylon gears in the transmission. The first indication that the gears are failing is that the transmission won't stay in the low-speed position.

    And the suggested "fix" is to mechanically force the transmission to stay in the low-speed configuration, and increase the damage on the gears???

    How is the solution to this problem not "stop drilling 1" holes in aluminum"?

    It's clear that this mill, for whatever reason, can't perform that operation without tearing itself apart. It doesn't matter if one thinks the mill "should" be able to handle the job, or that other methods take longer. The mill doesn't seem to care that anyone, including the operator, thinks that this is a reasonable thing to ask of it. Since it has happened more than once, it's perfectly clear (at least to me) that this mill cannot handle this task. Adding a mechanical "third hand" to force it to perform this operation will lead only to more frequent, and perhaps even more costly, repairs.

    My suggestion? (1) Fix the mill with the gears shown. (2) From now on use another way (and there are many) to make these holes that won't have the mill tearing itself apart. Either that or find another larger, stiffer, more powerful mill that will perform this operation at the speed you are looking for without damaging itself.

    Leave a comment:

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