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Thread: RF30 captive drawbar questions
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25th Mar 2020, 06:10 PM #1Golden Member
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RF30 captive drawbar questions
This isn’t a question about how to make it work, I’ve already done that. But my first design had some challenges and I’m in to version 2.
The original design broke because I had too large a roll pin in too small a diameter and the shaft snapped.
So I’m in to creating a new one with better tools and methods (I have a reamer and hex collet block this time).
Here’s the setup:
It’s a 12 rod, turned down to 7mm at the end. An M14 boot with a 7mm reamed hole and a top nut (yet to be made) that will be pinned to the shaft.
Questions:
1. I’m toying with the idea of using thrust bearings on the top and bottom of the captive bolt. Is this a good idea or unnecessary complication?
2. I’m planning on using a split pin to attach the top nut to the shaft. What’s the best way of drilling this hole and keeping all the parts aligned as I do it? I was thinking of using loctite and then drilling through the whole setup before breaking it apart, cleaning and pinning?
3. I was going to use a 3mm roll pin? Is that sturdy enough? Want to make sure I don’t break the top part like I did last time but make sure it won’t shear
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25th Mar 2020, 10:14 PM #2
In crane hook castle nuts they use a roll pin, then a solid pin inside that.
If it's good enough for safety of lifting equipment, it will be more than enough for a drawbar.
The solid pin strengthens the roll pin to almost a solid pin, but as most roll pins are HT, it will be even stronger.Using Tapatalk
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28th Mar 2020, 06:49 PM #3Golden Member
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A selection of roll pins have been acquired along with some thrust bearings. Going to go ahead with both and will have a go at using thrust bearings on the top and bottom of the captive bolt.
To drill the hole for the roll pin I was going to loctite the assembly together, pop it in a collet block, use an end mill to flatten the entry point, then spot drill and drill out to size.
I’m hoping the loctite will keep the assembly together as I drill through the whole thing and then roll pin it.
I’ve also got mega excited and finally bought some cold blue to finish it off.
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28th Mar 2020, 07:12 PM #4
If there is any slop in your quill keep the quill lock slightly locked, then you shouldn't need a flat to start it.
I often use my lathe center drills to start holes in the mill if I want them spot on, or drilling round bar.Using Tapatalk
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28th Mar 2020, 07:13 PM #5Golden Member
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Thanks Dave!
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28th Mar 2020, 07:30 PM #6
Hi Neevo, Guys,
Don't forget you can always use the steel ruler trick to centre the drill over the centre of the bar when setting up to do the drilling.Best Regards:
Baron J.
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28th Mar 2020, 09:07 PM #7Golden Member
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28th Mar 2020, 09:32 PM #8
Yes a center finder will help greatly, did you order a electronic one or a manual one, for these jobs I find a electronic one works best and is quicker.
If you want to do it before getting the center finder (China postage at the moment), place a 4 flue end mill in a chuck with the cutting edges aligned X-Y, then center it between your vice jaws when the job is tight in the vise.
It's a rough way but pretty accurate.Using Tapatalk
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28th Mar 2020, 09:34 PM #9Golden Member
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28th Mar 2020, 10:15 PM #10
I'm a visual guy as well, I can usually get something pretty spot on from visual looking at it.
If anyday you are up to buying a DRO and have some spare cash, it's really worth the investment at around $250.
I know we can't all afford it, but they really do make a huge difference in our home machining world.
Using your dials, touch off a jaw, zero it, then go to to other side to touch off, then half it, taking on backlash incount.
Just remember when coming back to over wind then come back to eliminate it.Using Tapatalk
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28th Mar 2020, 10:17 PM #11Golden Member
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DRO will definitely happen, just when, not if. I’m also set on a 3 axis. Just need a way to cleverly fit the z axis and have it hidden. I have a few ideas, but I also have plenty of projects I need to finish first.
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28th Mar 2020, 11:13 PM #12
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28th Mar 2020, 11:45 PM #13Golden Member
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Last time I got talking about the mill on here I bought a rotary table. Expensive exercise loading Tapatalk
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4th Apr 2020, 01:07 AM #14Most Valued Member
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4th Apr 2020, 01:51 PM #15
Just had another look at this one, after a clean it's a roll pin inside a roll pin.
It was gumed up with grease.Using Tapatalk
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