Advice on fixturing a part.
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  1. #1
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    Default Advice on fixturing a part.

    I want to make some simple hand knobs but I am not sure the best way to fixture the part. I know what I want to do I am just not sure it will work. This is the part from the Mcmaster Carr catalog McMaster-Carr At $6 each I can make them for my products for less. I have also purchased some off ebay that are cast but the fit and finish is not good they were $1.95 each. I have decided to try a batch and have the material coming my way tomorrow.

    Do you think making a negative in some soft jaws would work holding 5 at a time or would some of the parts go flying? I will post a picture of the CAD file. I plan to make the hand knob side first then flipping the parts in some soft jaws and cutting the round hub side where they will be broke into the 5 parts.

    Method 2 would be to cut the round hub side first and hold the round side in soft jaws and cut the hand knob side last. My fear is the parts won't clamp evenly and that will create an issue where some parts won't be clamped tight.

    hand-knobs.jpg

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    I’ve made hundreds of almost identical part. I blank them on the lathe then mill the knob side.
    Only 2 parts per vise or they WILL spin.

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    Quote Originally Posted by Booze Daily View Post
    I’ve made hundreds of almost identical part. I blank them on the lathe then mill the knob side.
    Only 2 parts per vise or they WILL spin.
    I don't have a CNC lathe just a manual one. I was afraid they would spin that is why I thought about doing the X side first but I am still afraid they won't clamp evenly. I was hoping to do 5 at a time per vise.

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    I think I just figured out how to do this and make a bunch at one time. I will make a negative of the hand knob side that spans both vises and holds multiple parts the hand knobs have a through 5/16" - 18 TPI tapped hole through the center made during op I will cut the hand knob side then put that into the negative with a matching hole in the center and use the threads created in op 1 to bolt each one tight into the negative fixture. The round hub side will then get machined in op 2 and I won't have to worry about them slipping in the vise.

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    Alternative option:
    Figure out who the manufacturer is for the McMaster part. McMaster will be there tomorrow and right, but they are more expensive.

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    looks like a mill part to me ,,, make them two at a time and do the bottom of the knob first opp then flip them over and hold the two stems and cut the finger groves ,,, two ops and there done ,,, a hour in the tumbler

    But I well do about anything not to have to turn the lathe on ,,

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    Definitely a mill part. Unless you have a beast of a live tooled lathe with a bar-feeder and parts catcher. That could probably run them for a couple days straight.

    Going to have to be creative, or dead-on-nuts sizing to hold more than two per jaw without some kind of individual clamp.

    Personally? I would do them in long strips.
    OP1, Long piece of stock in Talon-grip jaws. Cut both the round boss, and knob profile. Leaving as thin a "carrier" as possible.
    Cut apart on band-saw manually. Flip for OP2 in pocketed soft jaws. Face the carrier off, chamfer the hole and profile. Done.
    No deburring necessary.

    How many do you want to make, the process could be refined to pump them out quite fast.
    Like custom talon-gripped OP1 jaws that allow you to split the parts with an end-mill in process (eliminate the saw).
    Custom OP2 jaws that incorporate some kind of pressure equalization allowing more than two parts (several options on the market already).

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    I would blank them out on a lathe then make a couple fixture pallets with these McMaster-Carr. to do the the knob side in the mill. A back radius tool is good on these type of parts

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    Just to be different...

    Chuck up some round stock on the mill, use a key cutter on the hub and then cut off for done in one. Pull stock up to programmed dead stop and go at it again.

    Could work nice if you're outfitted right.

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    This is really interesting because I ordered a knob just like this in 1/2-13 a few days ago from McMaster. The problem was the threads weren't cut large enough and it wouldn't go on a 1/2-13 bolt. Also, they hardened the aluminum so tapping it didn't work either since it only wanted to take off a few thou.

    That was THE FIRST TIME that I got anything from McMaster that was wrong......

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    Quote Originally Posted by Booze Daily View Post
    I’ve made hundreds of almost identical part. I blank them on the lathe then mill the knob side.
    Only 2 parts per vise or they WILL spin.
    Nope. You are doing something wrong, or not finishing first op well, or ripping the crap out of the feeds for op 2. We regularly run 3-4-5-6 parts in soft jaws for second ops, all rounds from .75-1" or so diameter. And we run hundreds of parts like this. Last "big" run was for 400+ pieces. Haven't lost one in second op work yet since I have been here.

    I say OP can run 3-4 up, either way, just mill second op jaws accordingly.

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    P1, knob complete except for the top surface which is in the carrier. Cut from 1" bar held with Talon Grips (could also use 7/8" if available):

    knobs.jpg


    P2 is with soft jaws to hold the parts from P1, deck off the carrier, roundover the edges.

    You can scale P1 up as far as you like. I could do 12 at a time in my 2 vises.

    Based on the timings I'm getting from my CAM simulation, I can beat McMaster-Carr by a pretty wide margin .

    Regards.

    Mike

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    I run 12 up of this little part no problem. Similar setup to what was suggested in the previous post. The middle setup rounds the tabs, drills the holes and chamfers both sides. Then I just deck off the carrier and chamfer the back in the right hand vise.

    Sent from my SM-N960U using Tapatalk

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    I tried this with a little crescent moon shaped part and never had any luck. I started with 5 or maybe 7 per jaw, but one or two would always lift.

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    We run tens of thousands of these little bastards that way and only loose a handfull a year, most of the time it is because too many chips get around the leadscrew of the vise and the vise clamps the chips rather than the parts.
    img_7444.jpg
    img_7445-1-.jpg
    img_7447.jpg
    img_7448.jpg

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    The video shows how I make a similar knob. I start with bars for the 1st op, machine the wings and threaded hole, then screw them into matching pockets for the 2nd op with minimum waste and no need to tumble. The only change I would make is the 2nd op pockets don't need to be very deep. The number of bars I run at a time was driven by the aluminum I had on hand for the fixture and the number I need to make a year. I also really like that it fits in my vise without any fuss, like removing jaws and such.
    I could run the machine faster but then it would be faster than I can feed it so no point.


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    I have made my share of custom knobs with wings/finger grooves, etc.

    A live tooled lathe is my first go to.
    The second option would be to make the parts 1 & done, on the mill.

    Hold a strip of material long enough for multiple parts (via talon grips, or whatever) in the vise.
    Have enough material to completely machine the knob, and cut off, above the vise.

    Mill the round OD, mill the wings, drill & tap the center, undercut using a key cutter, and use a underside roundover (or chamfer) tool to ease the edges.
    Then run a slitting saw under the parts. (you can leave a 0.01-0.02" to not completely cut off [and lose] the parts.)
    Collect the parts and dump them in a tumbler for an hour or two.
    Done!

    Doug.

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  23. #18
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    I made the first batch of these knobs today. I made them in strips and cut the handle and drilled and tapped the hole in the first op. I made 2 fixtures to hold the knobs by the handle end and used the threads to hold the handle end into the fixture I made 2 fixtures so parts will be cutting continually after quickly changing them out in the vise I wish I had double station vises. The first op I get 12 parts half done cycle time is 9 minutes. The second op is 8 minutes and the fixture holds 24 knobs.

    20200601_165953.jpg

    20200601_155848.jpg

    20200601_171251.jpg

    20200601_185445.jpg

    20200601_205058.jpg

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    Quote Originally Posted by gundog View Post
    I don't have a CNC lathe just a manual one. I was afraid they would spin that is why I thought about doing the X side first but I am still afraid they won't clamp evenly. I was hoping to do 5 at a time per vise.
    Well.. fine, but... "too common"? The end product resembles something on the wall in the toilet supply valve section of any Big Box.

    Is that really the best use of your time, ingenuity, and machine resources?

    Human hand is a right adaptable device.

    If you have some flexibility in the product design, how about finding an extrusion you can buy in serious lengths, already "fluted", saw or turn and part-off, then deburr and/or polish . .if even it needs that much?

    Might even find it more comfortable, in use, as well as nicer looking?

    Mind .. if your product IS new handles for gaslight-era plumbing valves?

    Then I take it all back...


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    Quote Originally Posted by thermite View Post
    Well.. fine, but... "too common"? The end product resembles something on the wall in the toilet supply valve section of any Big Box.

    Is that really the best use of your time, ingenuity, and machine resources?

    Human hand is a right adaptable device.

    If you have some flexibility in the product design, how about finding an extrusion you can buy in serious lengths, already "fluted", saw or turn and part-off, then deburr and/or polish . .if even it needs that much?

    Might even find it more comfortable, in use, as well as nicer looking?

    Mind .. if your product IS new handles for gaslight-era plumbing valves?

    Then I take it all back...

    It is a knob not art work there is no place to install a feather to tickle your ass with. I make parts for my own business I have been using the same knob purchased from someone else for several years. Keeping cycle times down to make this part was the goal I did that for me it is a success. My customers were happy with the last knob and it does what it needs to do the goal is to make them with the least amount of effort which makes me more $$.

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