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Logan 11 threading what am I doing wrong.

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  • boats
    replied
    Jobs finished. Probably easier new rod new thread but junk axle on hand already threaded 5/8 11 rusty. Run the lathe properly cleaning up rusty thread easy, but must take the backlash out & make sure you set the tool right.

    Boats

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  • Bented
    replied
    I have taken for granted that anyone using a manual lathe understands backlash and will remove it accordingly.

    One of last weeks jobs, all dimensions on part #1 were spot on, the thread is supposed to be left handed however. Turned it RH out of habit (-:

    Leave a comment:


  • Paul Alciatore
    replied
    Using an indicator in this manner may be a good way to verify the thread lead, but you must be sure to take up any slack/backlash in the gear train before you zero that indicator. And also be very sure to take exactly one revolution, not more or less.

    I would prefer using a scratch test. Coat the work piece to be threaded with some blue marking die or with a Sharpie marker. Then run the threading as normal, but with the tool set to just barely scratch that die or ink. You can then hold a thread pitch gauge against the scratch marks to verify the pitch. This method will almost automatically take up any slack/backlash in the gears because you start the spindle rotation a turn or three from the beginning of the scratch and it will be more accurate because you will be checking across several threads instead of just one.



    Originally posted by Bented View Post
    A bit of advice.
    If you are a home hobbyist with a small machine and rarely single point threads, verify the lead before threading, you have all of the time in the world to do 1 job.

    Place a dial indicator in such a way that it will measure carriage travel, place the spindle in gear and engage the 1/2 nuts and rotate the chuck by hand measuring the Lead per Revolution.
    In this case .091 per rev.
    If the machine will not allow rotating the chuck by hand whilst in gear either because it is to large to rotate by hand or has a spindle brake take a skim cut first and measure the lead.

    Leave a comment:


  • danlb
    replied
    Yay! That seems to be a common mistake. There was a similar problem last year where the person had a HF 9x20 and was using the apron feed lever instead of the halfnuts. I'm tempted to label all the levers and knobs on mine just to be sure that I remember after a month or two away from the shop.

    Dan

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  • boats
    replied
    Well I cured the problem, operator error. On my old Atlas all feed was with the Half nut thread and between centers, did a lot of threading on it.

    Logan feeds between centers with a separate clutch Thread engagement with lever engaging the half nut. Operated properly it cuts threads like it should. I was using the clutch not the thread lever.

    Figured it out taking the garbage out. Last year cans lid hinge pin broke. Fixed it with a new pin from 50mm Scrap Delrin Ends threaded 3/4 - 10 & nuts . Looked at it and knew the job could only have been done on the Logan. Rod too large to pass through the Atlas Headstock. No doubt when the Logan was new to me followed the manual.

    Went back to the Logan and error was obvious. Good thing I don't do this for a living.

    Thanks all who responded & Dan gets the prize for figuring it out.

    Boats

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  • danlb
    replied
    The other thing that often screws up people when they seldom use a feature is extra optional controls. That lathe should have a selector for threading / fine feed. From another site with a similar problem I found this nugget.

    "Jon in Tucson, was right! For some reason I was engaging the clutch instead of the half nut lever...."

    Might be time to double check all the controls being used, both on apron and headstock.

    Dan

    Leave a comment:


  • old mart
    replied
    I have been known to do something like you are doing on purpose. The museums Smart & Brown model A can only produce threads up to 8tpi as standard. To get 5tpi, I doubled the speed of the leadscrew by changing the gears and then set 10tpi on the QCGB.

    Leave a comment:


  • wdtom44
    replied
    Hey Boats, have been waiting to see how you made out. As I said in my other post I think your leadscrew is turning too slow by 1/2. If you double it's speed in relation to the spindle you will get 11 tpi. I think that there are usually two different stud gears available for small Logans and South Bends. Something like 16 and 32 or 20 and 40. The threading chart probably shows which one to use for different ranges of threads obtained by the quick change box. In any case if you can double the speed of the leadscrew you should get your 11 tpi.

    Leave a comment:


  • J Tiers
    replied
    Originally posted by JRouche View Post

    I think Jerold is our Resident Expert Re: a Logan Lathe.

    Hit him up, I am sure he can help one way or anther. JR
    Phooey, I have a change gear machine, not a QCGB. Plenty here have Logan machines just like the OP..

    But I agree with the others, for what that is worth, double pitch suggests wrong gears.

    Leave a comment:


  • wdtom44
    replied
    Are there not some gears on the end of the lathe that can be switched around? It sounds like the stud gear is say a 16 tooth when it should be a 32 as it is cutting twice as many threads as the setting.

    Leave a comment:


  • JRouche
    replied
    Originally posted by boats View Post
    Any advise or comment appreciated.

    Boats
    I think Jerold is our Resident Expert Re: a Logan Lathe.

    Hit him up, I am sure he can help one way or anther. JR

    Leave a comment:


  • boats
    replied
    Thanks all, looking at photos is a kind offer. My old Atlas is in my sons shop now, will do the thread clean up on it. Finish up a couple pressing jobs then pull the gear box off the Logan. Meanwhile Gunsmith I know has a Logan like mine will run it by him too.

    Boats

    Leave a comment:


  • Bented
    replied
    A bit of advice.
    If you are a home hobbyist with a small machine and rarely single point threads, verify the lead before threading, you have all of the time in the world to do 1 job.

    Place a dial indicator in such a way that it will measure carriage travel, place the spindle in gear and engage the 1/2 nuts and rotate the chuck by hand measuring the Lead per Revolution.
    In this case .091 per rev.
    If the machine will not allow rotating the chuck by hand whilst in gear either because it is to large to rotate by hand or has a spindle brake take a skim cut first and measure the lead.

    Leave a comment:


  • Paul Alciatore
    replied
    The gears in most QC gearboxes are USUALLY arranged in a sequence from smallest to largest. A quick look inside the box should confirm that they are in that sequence.

    If it is a QC box with two setting arms, then the one with the smaller number of holes, a range setting, may have an out of sequence gear or two due to changing the external gears for some ranges or for a fine range for power feed.

    Some photos may be helpful here. The first one I would want to see would be the table of settings. And then the gear train from spindle to the QC box. Count the gears on those external gears and post those numbers with the photo.

    Leave a comment:


  • boats
    replied
    I always check with a thread gage before starting. This job, freshen up existing thread, ran a test on scrap 50 MM Delrin rod first. That showed the error. Checked and re checked the pin positions too.

    It may be I never actually cut a thread on this lathe, kept my Atlas 12 set up for couple years after buying the Logan and I don’t thread often. In the manual it mentions moving 72 and 36 tooth gears from stud to idler position. 72 is for cutting 4 to 7 pi. 36 the rest, Wrong gear ? Can see how that could cause It and my cuts spacing are exactly half desired.

    Back after I look into that.

    Boats

    Leave a comment:

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