First Real Project

[Kroll]

I call it my first real project that has to fit.So I give myself big C on this since the first shaft was way undersize and this one is little undersized but I can correct it with bushings.In couple previous post I had ask about getting that perfect finish then another post of feed/speeds then a 3rd on live centers which thanks to ya'll got lot of good answers.So in the pic I was trying to copy the old shaft but wanting the OD's to fit perfectly for couple gears which one has a woodruff key and the other has a bushing which I will press in and hope it fits the shaft better than what it does just by itself.Na guys I use a die for the threads,which that will be another big lesson for me in future.Guys I need to cut couple woodruff keys in this shaft with mill but again this be first for me and I am clueless on woodruff key cutters.How does a person measure these woodruff key slots so that the correct woodruff cutter can be order?I can measure the width but I don't know about the diameter.Any good sources for these cutters?

 

[Firstgear]

let mr. google be your friend!

Standard Keyway Practice

My question is about stand practice when cutting keyways. I know I can make it work, but I want to make it standard, if possible. Key stock is square. So, using 1/8" key as an example and cutting a keyway in a shaft and a gear, what is the point of reference for the depth of the keyways on...

www.practicalmachinist.com

 

[benmychree]

Look up in Machinery's Handbook, they give the depth for all the sizes of woodruff keys (there are a big bunch of them); the depth of the key is commonly measured from a flat that is cut with the woodruff cutter that is the same width as the cutter, you just sneak up with the cutter until contact is made, then move the piece back and forth while slowly feeding into the shaft until a mark is made that is the same width as the cutter, the cutter is then centered on the marking, the dial reading zeroed, and feed by hand to the finished depth, at least that was the way I was taught to do it, and have done for about 55 years now. Also, woodruff cutters are good for cutting straight keyways, they cut to size, unlike end mills which tend to pull to one side. The only drawback is that they leave a radiused run out portion at the ends; for larger keyways than woodruff cutters are commonly used for, large woodruff keys and straight keyways are cut with plain arbor type milling cutters, that is cutters without side teeth.

 

[mikey]

I need to cut couple woodruff keys in this shaft with mill but again this be first for me and I am clueless on woodruff key cutters.How does a person measure these woodruff key slots so that the correct woodruff cutter can be order?I can measure the width but I don't know about the diameter.Any good sources for these cutters?

Woodruff keys are sized by their width and length so measure the slot carefully. Imperial and metric keys are nominal and by measuring the slot on the old shaft, you should be able to identify the key that goes in it. Then you simply buy a woodruff keyseat cutter for that size key.

I only use Keo woodruff cutters because they are incredibly accurate. The fit of the key in the slot is an interference fit on the order of 0.0003-0.0005" and the cutter must be undersized by precise amounts to enable this fit; Keo cutters will give you that fit.

You must also use an accurate tool holding system with Woodruff cutters and I would suggest an accurate ER collet in a good chuck with a good nut. This is where the value of an accurate tool holder really shows because excessive run out of the tool will result is a loose fit of the key in the slot. Depending on what the key is locating this can be a problem. For example, the indexing collar on a cross slide leadscrew is usually kept in radial alignment with a Woodruff key. Imagine the problems you'll have if the collar can move around on you - not good.

The key seat must usually be cut to a prescribed depth. This is so that the key way in the thing that fits over the key will actually fit the key properly. If the key seat is too shallow, the key sticks up too high; if too deep then the component can wiggle around and again, that's not good. There is a formula and tables that give you the proper depth of cut. The discussion in Machinery's Handbook is woefully inadequate - a single paragraph. I'll try to find some time to write an article on cutting Woodruff keyseats that goes over how to calculate your depth of cut so you have the proper projection.

In the meantime, try to measure your slot carefully and buy the right keys and a decent cutter. I hope you have accurate collets because an end mill holder or an R8 collet is not likely to give you the tight runout control you are going to need.

 

[benmychree]

Woodruff keys are sized by their width and length so measure the slot carefully. Imperial and metric keys are nominal and by measuring the slot on the old shaft, you should be able to identify the key that goes in it. Then you simply buy a woodruff keyseat cutter for that size key.

I only use Keo woodruff cutters because they are incredibly accurate. The fit of the key in the slot is an interference fit on the order of 0.0003-0.0005" and the cutter must be undersized by precise amounts to enable this fit; Keo cutters will give you that fit.

You must also use an accurate tool holding system with Woodruff cutters and I would suggest an accurate ER collet in a good chuck with a good nut. This is where the value of an accurate tool holder really shows because excessive run out of the tool will result is a loose fit of the key in the slot. Depending on what the key is locating this can be a problem. For example, the indexing collar on a cross slide leadscrew is usually kept in radial alignment with a Woodruff key. Imagine the problems you'll have if the collar can move around on you - not good.

The key seat must usually be cut to a prescribed depth. This is so that the key way in the thing that fits over the key will actually fit the key properly. If the key seat is too shallow, the key sticks up too high; if too deep then the component can wiggle around and again, that's not good. There is a formula and tables that give you the proper depth of cut. The discussion in Machinery's Handbook is woefully inadequate - a single paragraph. I'll try to find some time to write an article on cutting Woodruff keyseats that goes over how to calculate your depth of cut so you have the proper projection.

In the meantime, try to measure your slot carefully and buy the right keys and a decent cutter. I hope you have accurate collets because an end mill holder or an R8 collet is not likely to give you the tight runout control you are going to need.

I would beg to differ on the issue of Machinery's Handbook being inadequate so far as woodruff keyseats are concerned; the tabular data gives depths for every woodruff keyseat, I think in minimum and maximum depths. Cutting a woodruff keyseat is not rocket science! So far as measuring the existing keyseat, one must realize that the measured length on the shaft is not the key length, it is always shorter due to the curvature of the key overhanging the keyseat, so what is measured must be lengthened to the next nominal size to identify the cutter that will be needed.

 

[mikey]

I would beg to differ on the issue of Machinery's Handbook being inadequate so far as woodruff keyseats are concerned; the tabular data gives depths for every woodruff keyseat, I think in minimum and maximum depths. Cutting a woodruff keyseat is not rocket science!

John, this stuff is old hat to you but for a new guy with zero experience, while it may not be rocket science it may as well be Greek. The depth of cut for a given key is given in the ANSI tables but then you need to go several pages deeper to find that you also need to account for the shaft material, M, above that depth of cut to figure out the total depth of cut from the surface of the work piece. The discussion in MH does not tie these things together well and unless you understand how the tables work you could very well under or overcut the key seat depth. The tables do give you min and max width of cut, which is helpful for determining fits and choosing a cutter but of course, they don't tell you how to do that, either.

There is no question that MH is an incredible data resource but understanding the information you find, now that is not always easy for a newbie machinist.

 

[mikey]

Kroll, I am attaching the pertinent tables from MH. In the file Keys and Keyseats, table 9 gives you the dimensions of all common Imperial Woodruff keys (Metric keys requires another discussion). You can find your key there. In table 10, find the width of the keyseat and also the depth; the width gives min/max figures and this determines how tight the fit of the key will be. The depth, called Depth B, is the depth of the keyseat below the curvature of the shaft. However, there is a tiny bit of shaft material above this Depth B that must be accounted for to get your actual depth of cut from the surface of your shaft.

In the file Finding M, you will see this illustration and explanation:



See that little sliver of material above D (this D is the same as Depth B from the ANSI tables in the Keys and Keyseats file)? That sliver is called M, and the table in the file gives you this M-value for different diameter shafts. The problem is that YOUR shaft may not be in the table and while the difference between your shaft and the closest one in the table is negligible, it is simple to calculate if you choose to do so. Machinery's Handbook gives two formulas to calculate M, the simplest one being:

M = E(squared) / 4S, where E = width of your key and S is the diameter of your shaft.

You simply solve for M and add it to the Depth B from the table; that is your actual depth of cut from the moment your cutter touches the shaft.

An even easier way to find M is to use an online calculator: http://www.cncexpo.com/KeywayArc.aspx

So, you have the info you need to ID the key, the dimensions of the keyseat and your depth of cut from the surface to the bottom of the keyseat. If you are not sure which cutter to get, I would suggest you email Keo and ask them to advise you in choosing the right cutter based on the data you have. They are extremely helpful and quick to respond.

Let me know if any of this is unclear.

 

[benmychree]

John, this stuff is old hat to you but for a new guy with zero experience, while it may not be rocket science it may as well be Greek. The depth of cut for a given key is given in the ANSI tables but then you need to go several pages deeper to find that you also need to account for the shaft material, M, above that depth of cut to figure out the total depth of cut from the surface of the work piece. The discussion in MH does not tie these things together well and unless you understand how the tables work you could very well under or overcut the key seat depth. The tables do give you min and max width of cut, which is helpful for determining fits and choosing a cutter but of course, they don't tell you how to do that, either.

There is no question that MH is an incredible data resource but understanding the information you find, now that is not always easy for a newbie machinist.

This is why, in an earlier post, I said that you feed the cutter into the shaft and feed back & forth until you get a flat the width of the cutter, then feed to the final depth from that flat, and the flat is also used to center the cutter on the shaft; not exact to the thousandth, but good for nearly Any practical purpose.

 

[mikey]

I know what you mean, John. You're essentially cutting off M, which is what a lot of guys do so that the depth of cut in the table is directly usable. What I was trying to do is to help Kroll (and others) understand the information contained in MH. It isn't difficult once you figure out what information actually matters; its the figuring part that gets you.

 

[benmychree]

Sometimes, there is the tendency to overcomplicate things, all one has to do is consult the tabular data in MH (for depth), cut the flat, center the cutter on the flat, and cut to the depth indicated. I wrote the page number in the back of my MH for the table of dimensions of the myriad numbers of keys, so I can just flip to the page. I made the column with the depths bold with a ball point pen to make it easier to spot the numbers that I want (depth). I don't cut nearly so many woodruff keyseats as before I retired, BUT I'M READY AT A MOMENT'S NOTICE! I also use woodruff cutters to cut straight keyways sometimes, as they cut to accurate size; for larger widths, I use a plain milling cutter. In the shop where I apprenticed, we used end mills to cut nearly all keyways; it was a PITA, especially doing it on a horizontal mill.