Previously I published a similar project about a mandrel for a Yamakawa 80mm 3-jaw chuck with a set of toolmakers mini jaws (see http://www.homemadetools.net/forum/c...0262#post72147 ). The new mandrel in this posting is very similar in size but is designed to hold a 5” 4-jaw Bison chuck in a larger 3-jaw chuck. The small 4-jaw chuck had been used on my 7" mini lathe but this lathe is now used almost exclusively for small collet work using ER32 collets. Now while using the 12" swing geared head lathe, there are times when a smaller 4-jaw chuck with a mandrel would be much easier to install into the D1-4 mounted 6” 3-jaw chuck than swapping out the 6” chuck for the heavier 8” 4-jaw chuck.
The 5” Bison 4-jaw chuck now has a mandrel machined from 1045 alloy carbon steel 3.25" round bar stock. The mandrel has an overall length of 3.3” and the shaft dimensions are 1.5” dia. x 2.5” long. The chuck is attached with three M6x1 studs and nuts on the larger end that is 3.20” dia.x 0.375” thick. In addition the larger end has a 0.110” deep step that inserts snugly into a recess in the back of the 5” 4-jaw chuck. The three holes for the studs were located with a inscribed circle marked while still mounted for machining in the lathe. The center-to-center cord was calculated and used to locate the three holes centers with a pair of dividers. The bolt holes are 0.257” dia. (Letter F drill). A 0.700” thru hole runs down the center of the mandrel.
Below are photos taken while machining the mandrel
Thank you for looking,
Last edited by Paul Jones; 12-05-2016 at 09:38 AM.
Nice project and great documentation Paul. Just curious about doing bolt circles accurately. You mention about laying out the centerline, but how did you divide and drill the holes? Did you do it on the lathe or? I'm trying to figure out how to do bolt circles especially when there is no center point to go by, as in the brake rotors on my trike.
Seems like some kind of dividing setup for the lathe head like Christophe or Olderdan would be the ticket with some kind of adapter for drilling.
n = number of holes
r = RADIUS (half the diameter) of the bolt circle
a = 360 / n = angle between adjacent holes
Calculate x,y coordinates, measured from the center of the work, as follows for k = 0,1,2, ... up to k = n-1
x = r * cos (k * a)
y = r * sin (k * a)
Last edited by mklotz; 12-05-2016 at 10:14 AM.
Home Shop Freeware
Thank you Paul for another great write up and pics. The idea of these mandrel chuck in a chuck seems a good way to go, especially having to go to an 8" to get the 4 jaws...almost need a hoist for something like that. Think you and JR have started a trend. I particularly liked that you used the "Old School" divider technique to determine you hole centers on the BC. It was one of the first exercises I used to teach drafting students. If students get the geometry into their hands and minds then moving to CAD is a piece of cake. What can be done with a pencil, ruler and compass has always been near and dear to me. Thanks for sharing that here.
I am curious how that 5" bison ran on the mini. Any reduction in power or other issues? I've been wanting a 4 jaw for ages but was considering the 4" LMS to match my 4" 3 jaw. Bison's are very nice chucks and used them on my Drill Machines but may be out of my price range.
P.S. Not to undercut Marv's great posting or his Calculator C-Bag, but I use a program called ShopCalc by Richard Sanders up in Canada. It is a VB program that will run in Win7 and calculates all this stuff including X/Y bolt circles. I would also bet there is an app for your Apple Tablet. It might be worth your while though to give the divider technique a try.
Always do right. This will gratify some people and astonish the rest.
Thanks Marv for the formulas.
C-Bag, I inscribed the bolt circle center line while the mandrel was still in the lathe chuck. I had just finished machining the boss on the end the mandrel and knew its exact diameter. Using the boss as a reference edge, I remove the backlash from the cross slide, and loosened the dog point set screws holding the lathe tool holder to allow pressing a sharp pointed lathe tool against the boss and re-tightened the set screws. This allowed me to know exact location of the lathe tool point and I then backed the cross slide out to one half the difference of the bolt circle diameter minus the boss diameter. Lightly plunging the lathe tool into the mandrel front surface scribes the bolt circle.
I had previously measured the bolt circle on the back of the 5" 4-jaw chuck by installing two tight bolts, measuring the separating distance and then calculating the cord distance, and finally the bolt circle diameter. The 3 hole spacing on the mandrel was done with a spring divider set to the the cord distance which is bolt center-to-center distance. I use a Machinist Calc Pro model 4087 to calculate the bolt pattern dimensions. I use this calculator in my shop for many machining and layout calculations.
The three holes were drilled in the mandrel with a dress press and not by x-y coordinates or indexer on a milling machine. I use a prick punch, followed by a center punch, and a sharp 1/8" diameter spot drill, 1/8" drill, and finally the Letter F drill. I can usually drill the holes right on or within 0.002", so I don't bother with a milling machine unless everything has to be exact.
In the case of your brake rotors, I suggest making a disk with a boss that fits into the center hole and has a small spot drill dimple in the center. Use spring dividers to scribe the bolt circle, and then lay out the bolt holes center-to-center distances with the spring divider, and go around in both directions to double check your work. Prick punch and center punch the holes. Use the brush applied Dykem for a very dark contast and you can check your inscribed arc intersections from both directions for quality control before using the prick punch.
Last edited by Paul Jones; 12-05-2016 at 01:43 PM.
You have a good concern about running the 5" 3-jaw chuck on a mini lathe with a 7" swing. I know others had simialr concerns when I first published the article about mounting the chuck on the mini (see http://www.homemadetools.net/forum/a...4269#post18042 ). I could not see any reduction in power (monitoring the RPMs while machining is the main reason I installed tachometers on my lathes) but the extra mass really helps with the rotational momentum and I don't think the extra mass is harming the headstock bearings. This is no longer an issue now that the mini is run win an ER32 collet for most work and no need for the 5" chuck on the mini lathe.
I bought the 5" Bison 4-jaw chuck in 1993 and it didn't seem too expensive at the time but Bison chucks today are pretty expensive. Last year I bought an 8" 4-jaw Fuerda/Gator D1-4 mounted chuck for the 12' swing geared head lathe and found the quality to be excellent. There is great story at Practical Machinist about how the Fuerda/Gator company was started and the quality control used to inspect their chucks (see A story about Bison & Fuerda (Gator) chucks ... ). This Black Friday, I ordered a 6" 6-jaw set tru Fuerda/Gator chuck at a considerable discount and looking forward to making it my main chuck on the 12" lathe.
Last edited by Paul Jones; 03-20-2018 at 09:52 PM.
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