Knurling with QCTP

wawoodman

himself, himself
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I just got a CDCO tool post. A local fellow supplied me with a nut, to fit the compound on my SB 10K. (Thanks, Mike!) Just for fun, I tried out the knurling tool that came with the QCTP. As I brought the tool up to my blank (a piece of 3/4" 12L14) I could not keep the toolpost from rotating away from 90°. I have the bolt as tight as I dare to make it! I have checked to make sure that the nut is locking in the compound and is not bottoming out on the post.

Any other ideas? A scissors knurler is on my list, but in the meantime...
 
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You could stimple the underside of the toolpost and the top of the compound to add traction. I beadblasted the top of the new compound slide for just this reason.

As stated above the scissor type is better as the load is only on the knurls and not on the spindle bearings and the tool post.
 
As was suggested earlier a piece of paper under the post might help. I would recommend gasket paper.
Does your tool post have a threaded hole in one side? A lot of them do. Could a bracket be made to stop it from slipping.
I would be more concerned about wear on the cross feed nut than the spindle bearing from using a bump knurling tool.

Terry
 
When we are dealing with a CNC machine that weighs upwards of 2 or 3 tons, the bearings are that much tighter, and the spindle is that much larger in diameter, and no they would not see any deflection from the use of a Bump Type knurler operating on the small diameters of stock that most things are knurled.

Now when we start talking about a Southbend with its bronze bearing shells, that are known to wear over time, or even the small lathes like the 9x20 imports, well Scissor knurlers are about the only way to get a good consistent knurl as the bearings start out being less than up to snuff and get way worse with wear. Also if the knurl is on long stock, then we see deflection not so much in the bearings, but in the stock. This again is where the scissor knurlers make more sense as they do not deflect the stock, they act like a follow rest.

In this case I believe that both Playtpus20 (Jack) and mnmh (Ed) have valid points.

As for Mike's original question, my QCTP has a SHCS that goes though it and threads into a hole that is drilled and tapped in the T-Slot Nut and it prevents any movement at all of the QCTP. Mind you 90% of the time, I find that I want to have the compound and tool post at other angles than these two holes to line up, so I rarely ever have it installed.

Here agian the scissor knurl has advantages as it will not put as much force on the QCTP which will help to prevent it from spinning the QCTP under the knurling load.

What I would do is spread Prussian Blue, or maybe even better just rub the surface with Sharpie ink and rotate the QCTP around. this will show if there are any high spots that need to be stoned down.

Walter
 
Mike,
Get the scissor type. I have mine set up on my QCTP on my 13" TurnPro and it is simple and easy to use. I haven't used the old bump types since.

Randy
 
1200rpm link=topic=1618.msg11881#msg11881 date=1303728590 said:
you checked to see if the nut was hitting the post but did you check to see if the bolt was threading too far through the nut and hitting the bottom of the T slot? i apologize if i am stating the obvious and you have already checked that.

You know, I don't think I did. #1 on the list when I get down there this morning!
Thanks.
 
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An EE is a pretty substantial lathe. You can probably use that combo for another 100 years 8^)
A SB10 is not near as substantial. I'd get away from the bump on the SB and go scissors. Why risk your spindle bearings?

Randy
 
Well, I am prejudiced against bump knurling tools. Mainly because I have used the scissor type now for about 25 years, so I see the advantages. I have a couple of bump style, but they never get used. Considering the pressure required to upset the metal in a knurl, the design of the scissor style logically must absorb the lion's share of it in the pivot pin and the axle pins of the rolls. In a bump style, the tool is simply brought to bear against the material until enough pressure is there to upset the material. All of that force is pretty much absorbed by the spindle and tailstock, if used, along with the axle pins of the rolls. Also, to knurl long pieces, a bump tool is out.

Granted, lathe bearings are, as a rule, robust, and take an enormous amount of pressure while taking heavy cuts, or during large drilling. I'll never say that the bearings will not tolerate the pressure from old fashioned knurling, but if there is a method that reduces that pressure, I'll use it.

Interestingly, several years ago I did a comparison between the two styles of tool on a small CNC, a Kia Seiki of some sort (about 20 hp), I forget the model. I was most interested in the electrical load. As I recall, using the scissor type tool dropped the motor load, as displayed in the current draw, by about 20%. That's not a measure of bearing stress, but I have to believe that if the motor load is down, so is the spindle stress, and hence bearing stress.

One note about adding paper under a toolpost. Use a couple of strips of 80 grit instead of plain paper.
 
It's very possible that the top of the compound is not flat, or has a ding or a chip impressed in it. It's fair to take a fly cut across the top. Also, it's worth a look at the bottom of the TP. Both should be flat.
 
I shouldn't say this but I flattened mine with a file. Been working great almost 2 years now. tommie
 
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