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Knee Raising Crank Handles - BP Type Mills

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petertha

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#1
This may be the most obtuse question ever posted, but why does the crank handle on a mill have to weigh 20 pounds or whatever it is, cast from thick section iron like it could serve double duty jacking up the rear end of a Sherman tank? I mean has anyone ever broke a handle raising the knee cranking on a worm gear? I'm not a weakling but it just occurs to me (on my new mill which is a nice step up from my RF-45) that nudging in the last couple thou with that medieval club, seems kind of out of place? I can apply sufficient torque with one hand choked up practically to the shaft. I understand the leverage factor if you have heavy fixtures & parts. Or maybe you are cross training for the Model-T engine cranking Olympics. But since the hub has on/off cog teeth, how about a mini wheel for the fine stuff? Or light weight, short span symmetrical handle more like table handles that doesn't want to flop on one side due to the weight? Or a 1/2 pound carbon fiber handle like a German bike pedal crank? OK, that would cost more than the DRO & the tarrifs would be brutal. Joshing aside, maybe someone can enlighten me.
 

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pstemari

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#2
Even with nothing on the table, you still have to lift the knee, which is a pretty massive casting, the saddle, and the table. I'm guessing that's at least 300–400lbs. Granted, mechanical advantage with the crank is about 560:1,

You could certainly make an adapter to use something like a small steering wheel as a spinner crank, but leverage might be an issue. A 12" dia wheel has 1/3 the advantage of an 18" crank.

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petertha

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#3
So you're saying they had it right 75 years ago and me with my 2 weeks of experience on this machine should just adapt! :) I think it just takes getting used to the light touch on the fine increment adjust & careful re-engaging the cogs if the handle is in the way.

One positive thing I notice lifting the big weight as you say, it mostly stays put. My RF-45 by contrast was fixed table, head came down the dovetail & quill was more of the go-to Z setting device. So for accuracy you always lock everything up. It wasn't too bad but, always a bit of couple thou guessing game what you dialed in vs. what came off. The BP clone is more substantial & seems to stay where its put.

OK cancel the order on the carbon fiber crank. LOL
 

Tozguy

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#4
What you need is a power assisted crank. In the ole days steering wheels on cars were huge (by today's standards). With the spread of power steering systems today we can turn a small steering wheel using one finger. So maybe the newer electric power steering systems on cars can be adapted to a mill. If you work something out like that it would help us all.
In the mean time we are saving on gym membership fees by getting our exercise from day to day life at home.
 

projectnut

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#5
The 9"x42" table itself weighs a little under 300 lbs. The knee is again very close to the 300 lb. mark. The maximum weight that the table can handle is listed as 750 lbs. In total the crank could be lifting up to 1350 lbs. Even with a 560:1 ratio it takes some power to lift that size load. I doubt a carbon fiber handle or small wheel would be up to the job.

The replacement Bridgeport handle sold by Hardinge only weigh 2.05 lbs. I have seen aluminum handles, but the downside is they wear quickly by comparison. I have also seen adaptors for cordless drills, but have no idea of their durability.

There are companies that make power feeds, but they are relatively expensive. Travers Tools sells several ranging in price from a little over $500.00 to over $800.00. Precision Mathews sells one for their machines at a little over $300.00

It isn't hard to get precise positioning with the crank handle. When getting close to the required depth I reposition the handle so the weight is on the downside of the turn (from 1:00 o clock to 4:00 o clock). Then gently apply pressure to the top of the handle while watching the dial. It doesn't take much effort to get the precise graduation. If you don't like reading the dials you can always install a 3 axis DRO. DRO Pros sells several different ones ranging from $780.00 t0 $1,700.00

http://www.dropros.com/Electronica_...m#Electronica_Magnetic_Scale_3_Axis_Mill_Kits:
 

ttabbal

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#6
I find that the handle on my Bridgeport is quite accurate. I have a DRO installed and positioning in the tenths is possible with care.

Right now I'm using a 3D printed drill adapter for power feed on the knee. It's sure a lot nicer than cranking long distances. It has a hex head, I bet you could use a stubby wrench on it for more precise adjustments if needed.
 

JimDawson

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#7
I have a knee power feed and a hand wheel. I wouldn't want to hand crank the knee too far, but for final adjustment it works fine. Easy to dial in to that last tenth.
1542383157414.png
 

Winegrower

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#8
Of all the annoying things in my shop the knee handle is pretty far down the list.
 

Dabbler

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#9
Peter, you are right. it is something to get used to... One Excello I used for a while needed an act of Parliament to raise the knee at all. I really wished for a longer handle on that machine. Poor maintenance and thick way oil made that thing a 'beast'!

It is very nice you have such a smooth machine - so make a 12" or 14" aluminum handle. If it wears out, you can always make it again, after all, you know someone with a mill!
 

Bob Korves

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#10
To try to hit my number, I find it works better for me to lower the knee a bit too far, and then hit my number while raising the knee, not when dropping it, which does not work well for me and my machine at all.
 

petertha

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#11
It isn't hard to get precise positioning with the crank handle. When getting close to the required depth I reposition the handle so the weight is on the downside of the turn (from 1:00 o clock to 4:00 o clock). Then gently apply pressure to the top of the handle while watching the dial. It doesn't take much effort to get the precise graduation.
Thanks, that is the technique I am gravitating to. I do already have power feed on the lift axis. Its not that my lifting forces are that high (yet), but it certainly takes the monotony of spinning it up & down a longer displacement like to accommodate tool changes. My comment/question was more about the finesse bit of last couple thou & hitting the mark, either by dial or DRO. I'm just getting used to the workflow of this new machine & have been taking the handle on/off mostly to get it out of the way. So even re-engaging the hub teeth & with the handle cantilevered, seemed like potential to move it off its mark. I think make gravity your friend & keep the handle pointing mostly downward is smarter. I'll figure it out. Thanks for the useful comments.
 
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BGHansen

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#12
Not adding anything here, but seems like someone with one of the 1/2" cordless drill driver adapters could put a torque wrench on the knee adapter and measure the torque required to move the table. Estimate double the torque assuming a load on the table equal to the weight of the table and knee. That'd tell us definitely what would work for an alternative to the typical crank.

One thing that got my jaw to drop was the first time I saw the drop links on the 2007 Cadillac CTS produced at the Lansing Grand River plant in Lansing, MI. The drop links go from the stabilizer bar to the control arms. They had ball joints on either end, but the link itself was made from glass filled nylon. The warranty for fractures was the same as the previous steel cans/rod version.

Bruce
 

pstemari

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#13
To try to hit my number, I find it works better for me to lower the knee a bit too far, and then hit my number while raising the knee, not when dropping it, which does not work well for me and my machine at all.
Yeah, for reasons similar to why climb milling can just problems. When you push up, the forces are balanced and there's no slop. When you lower the knee, you're moving the support down, introducing slop, and trusting gravity to push the table down and take the slop back out. It's entirely possible for it to stick a bit and then fall down to the support.

You always get more precise positioning when two forces are acting in opposite directions, vs two forces pushing in the same direction, with the slop changing sides whenever one force pushes a bit harder than the other.

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RockingJ

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#14
The longer length aids in finer adjustments. The heavy mass also helps when making fine adjustments, a small tap doesn’t move the handle very far, where a much lighter handle would be moving much further.

At least that is my take on it!


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