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Adding a 4th axis to my mill
« on: March 13, 2012, 07:18:52 PM »
I have been awed as a student of Mr. Simpson's (Simpson36) 4th axis work. I've watched each of his videos at least once. Some several times. I am so inspired that I needed to try my hand at making my own 4th axis. I was previously considering making my lathe cnc, but the 4th axis added to my mill will fit the bill nicely. In fact I made a couple of items for a medical facility not long ago, and a 4th axis would have cut the machining time by 75% easily.

I've got one spin indexer in house that I need to tear down to see if it's true enough for this project. I'll have to order another one for the tail stock too. Since the servo motors can handle something  around 2400 in-oz, then I think a steep reduction will hold difficult work very still and allow 300-600rpm for turning down material. I'm hoping that this design will not require a brake.

Here is the first prototype cad rendering using Rhino 2.0.

« Last Edit: March 16, 2012, 05:19:57 PM by Overloaded »
Re: Adding a 4th axis to my mill
« Reply #1 on: March 14, 2012, 11:52:19 PM »
I tore down the indexer today and wiped it free of all preservative oil. Man that stuff smells. As it turns out this particular spin indexer is exactly the same make and model as Steve had in his early prototype days. That was a surprise. I hope the 5c spindle is in better shape than the one he had or I get to repeat the buying pattern too. Steve reported that the bearings did not slip over the shaft easily.

I semi carefully drew up the 5c spindle in this rendering. It interacts with so many other parts. I wanted to make sure it would clear everything. I downloaded the shaft collars in 3d iges format from McMaster. Same with the ball bearings. I am convinced that I should use 40 degree angular contact bearings instead of deep ball bearings. Angular contact bearings are the same that were used when I rebuilt my Bridgeport head. They could last forever since they are designed for thrust loads. But the 4th axis is not as severe duty as the Bridgeport. So we'll see. I just made up the pulleys. They are dimensionally accurate. The tooth patten was just made up quickly. I had to slide the front wall forward and that eliminated the flat washers, so that end of the spindle stayed flush with the end of the base. The updated spindle model caused these changes. At least if a chuck gets installed it won't interfere with the base.

I still need to draw up the collet knob and threaded tube for the spindle. I also need to slot the back wall to move the motor to allow adjustable belt tension. A cover, bolt holes and other details are still missing.

« Last Edit: March 16, 2012, 05:21:39 PM by Overloaded »
Re: Adding a 4th axis to my mill
« Reply #2 on: March 15, 2012, 02:57:24 PM »
Bearings. It turns out I could not find 40 degree angular contact bearings that have rubber seals, anywhere. So I went with radial ball bearings with rubber seals after the SKF engineer told me that their line of 6200 series bearings have an axial load rating that is 50% of the radial load rating.   I was surprised that it was that high, but happy. That makes these bearings relatively cheap since they are so common. Higher cost bearings are usually higher rpm and have increased clearances and special low expansion balls for the higher rpm he told me. These bearings are 6209-2rs1. They are 45mm id x 85mm od x 19mm thick. So far my rpm limit if I was lucky will be 1000 rpm. More likely 300-400rpm. I have to do some testing of these servomotors for top speed to see how they will do. Maybe I can back calculate the rpm since I use the same motors for the cnc mill. If usps is any help, the bearings should arrive this Saturday. That way I can see how well they fit the od of the 5c spindle.

Thinking out loud. 135ipm. 20,000 pulses per rev. 20 turns per inch. Hmmm. 135ipm x 20 turns/inch = 2700 turns per minute or 2700 rpm. Hmmm. Much higher than I thought. And that 2700 rpm is at the motor while moving a heaving table and long ball screws. Although there is no cutting load. The limit for rpm so far is the pulse train out of the parallel port. My break out board is only 3 axis output. I'll need something more complex for this project. With a 5:1 belt reduction, 2700rpm becomes only 540 rpm at the spindle. 3:1 the rpm is 900. I don't think I turn more than about 400rpm on my lathe anyway. I'll double check that. Anyway, the rpm at the spindle with steep reduction I plan is slow. But the first project will be cutting delrin. So high rpm is not a requirement. There should be enough movement in the motor mounting to allow several different pulley sizes.

I tried fitting some 5c collets to the spindle last night. Not much success at first. The indexing pin was far too tall. So I reached in with a dremel and knocked it down some then deburred it the best I could. After some more fiddling it tightly fits a 5c collet now. The id of the spindle is the collet area seems to need some smoothing with scotchbrite or equivalent.

Just added the 5c collet knob and tube shaft. The knob was easy to design. I took the main diameter furnished with the indexer then subtracted 6 1" diameter rods inset just .125". This gives a nice gripping feature to the knob. But without super sharp edges. I'll had a hole for using a lever for added tightening as I have seen in the past.
« Last Edit: March 16, 2012, 05:14:54 PM by Overloaded »
Re: Adding a 4th axis to my mill
« Reply #3 on: March 15, 2012, 04:12:40 PM »
Bearings, pulleys, and a belt are on their way!  Hope to have the bearings Saturday so I can see how well the spindle fits them. Now I'm off to eat and hunt for aluminum stock.
Re: Adding a 4th axis to my mill
« Reply #4 on: March 15, 2012, 07:05:28 PM »
Picked up a 25lb 1" aluminum plate just a bit ago. Their saw was down. Cutting the parts from this will be fun. Will be enough stock for the head unit. Probably need a bit more for the tail stock, that's not designed yet.

Re: Adding a 4th axis to my mill
« Reply #5 on: March 16, 2012, 02:17:30 PM »
Added a few details to the head stock. The tail stock is started.

« Last Edit: March 16, 2012, 05:23:52 PM by Overloaded »
Re: Adding a 4th axis to my mill
« Reply #6 on: March 16, 2012, 03:06:05 PM »
If anyone knows the code to make these pics smaller and clickable, I'd really appreciate it. These pics are just taking up far too much thread volume.

Re: Adding a 4th axis to my mill
« Reply #7 on: March 16, 2012, 05:09:07 PM »
Hi Mike, nice work !
For the pics., use the REPLY button then Additional Options then browse to your file (of the types listed) and attach it instead of embedding. Best to resize them to about 800 x 600 first.

I did your earlier ones, hope they are OK.
« Last Edit: March 16, 2012, 05:28:18 PM by Overloaded »
Re: Adding a 4th axis to my mill
« Reply #8 on: March 16, 2012, 05:44:50 PM »
Thanks Russ! That's so much cleaner!!


Offline Dan13

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Re: Adding a 4th axis to my mill
« Reply #9 on: March 17, 2012, 03:15:35 AM »
Nice work, Mike.

50% axial load for a deep groove ball bearing... sounds too much to me too. Hope he knew what he was saying ;)