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Spline Cutting

12/06/2008 8:16 AM

We have a general machine shop, manufacturing large machines.

We are about to introduce a machine, for which we have to cut splines in one part. The component is high precision and but for the spline, everything can be done in house.

We do not have any experience in spline cutting (absolutely)

We have CNC-VTLs (with and without live spindle) , Center Lathes and Horizontal borers.

The component minus the spline is going to be macined in the CNC VTL (with live spindle)

Almost all the sites recommend broaching for the spline cutting.

Is it possible to use the existing machines (preferably the CNC VTL) for the spline cutting ? - this will allow us to machine the whole component in one machine and one setting.

The load is not high enough to invest in a broaching machine (the basic component is very large - about 1.2 m dia and 1.4 m hight , though the spline end of shaft is only about 400 mm dia and 70 mm spline length (spline class 8f of DIN) ?

We can not send the component for only spline cutting (possibility of damage in transport is high) and it may not be worth-while to block our capacity and out source the whole machined component only for one operation constraint.

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#1

Re: Spline Cutting

12/06/2008 10:03 AM

It certainly is possible to use CNC with a milling head and tool to cut the splines. Accurate indexing will be the critical part of the set-up and operation as this established the position of the spline on the circumference. This part of the operation will be time consuming but absolutely essential

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#2
In reply to #1

Re: Spline Cutting

12/06/2008 11:34 AM

The VTL we are now procuring is with c axis positioning feature with positioning accuracy of 7 arc sec.

The problem is as I see, the milling head must be tangential to the diameter. However the VTL will have the axis through the diameter of the component.

That case the only option is the HB - The accuracy of B axis for this we have to check up.

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#3
In reply to #2

Re: Spline Cutting

12/06/2008 11:32 PM

Internal or external spline? Straight or helical? I assume you are talking about an internal straight spline. External is simple with a 4 axis milling process and the requisite ability to grind the cutter to the correct tooth form.

An internal straight spline is best cut with a broach. However, the special broach can be very costly. Lacking that capability a shaper with a dividing head is a way to do it; but the labor content of the job will be considerable. This can even be done on a lathe with an indexible spindle; but the labor content is even greater with hand feeding the carriage.

A 4 axis cnc mill could do this with the spindle locked in one rotational position and the special groove shaped tool mounted in a boring head. This assumes the work piece can be rotated on the 4th axis.

If this is not the case then you will have to be more creative with your tool making and put the 4th axis control into a rotary table with a tool holder mounted thereon that can be rigidly mounted separately to the spindle structure. This does the indexing for each spline while the y motion of the workpiece on a "tombstone" accomplishes the cutting motion and the feed for each groove is done by moving x and z components as appropriate to the angular position of the spline to be cut. This will be a slow process; but less time consuming and less subject to operator error than a manual machine process.

In any case special single point cutting tools will need to be ground by your tool maker to accurate contours especially if the spline is an involute form.

Ed Weldon

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#4

Re: Spline Cutting

12/07/2008 6:22 AM

I assume you want to cut external splines on the spindle. We used to cut such splines on Gear Hobbing Machine or Gear Shaping Machine. You can get it cut on such CNC machine by the sub contractor having spare capacity. You need to buy Hob/cutter for spline cutting if splines are non standard.

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#5

Re: Spline Cutting

12/09/2008 1:12 PM

We use a gear shaper to cut internal splines, we also use keyseating machine sometimes.

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#6

Re: Spline Cutting

12/11/2008 5:37 AM

You need a "Spline Hob"

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#7

Re: Spline Cutting

12/17/2008 11:31 AM

I'm not sure what the size of your spline is but you may want to consider 'on machine broaching', or rotary broaching.

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#8
In reply to #7

Re: Spline Cutting

12/17/2008 7:16 PM

Thanks peter08, that just broadened my machinery horizons.

BAB

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#9
In reply to #7

Re: Spline Cutting

12/17/2008 8:58 PM

Peter08 -- I went to the rotary broaching website and studied it including the "how it works" part; but I'm still missing something. How that thing removes metal is still a mystery to me.

Ed Weldon

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#10
In reply to #9

Re: Spline Cutting

12/18/2008 9:41 AM

I know it's not the easiest thing to explain, I've been trying to for years. But, imagine that you're a kid again :), and you're pushing a star shaped cookie cutter down into a slab of play-doh. To push it straight down becomes too difficult, so you shift your weight on the cutter, and pivot in a circular motion so that all your weight is pushing down on only one corner at a time. Rotary broaching essentially does the same thing, but in steel. And wala! A star is born.

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#11
In reply to #10

Re: Spline Cutting

12/18/2008 11:22 AM

Peter08 -- Thank you.

One of our number here says something to the effect that how well you understand something is inversely proportional to the number of words you use to explain it. Looks like you rate high by that measure.

So am I correct in assuming that the depth limits for this process are due to the problems of clearing the chips? Does it help to maximize the depth of the pilot hole to make a place for the chips to go?

Thanks again, Ed Weldon

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#12
In reply to #11

Re: Spline Cutting

12/18/2008 11:33 AM

Yessir! You are correct about the chips. That's part of the problem with depth limitations. There's a few mechanical issues as well, for instance: the broach has to have a back taper, so that the sides of it don't crash the sides of the part as you pivot through the hole. Therefore, the broach can only be so long until it becomes too narrow and weak for broaching. There are similar issues with the tooling. Your pilot hole comment was right on, you need to have room for chips and any fluids that may get trapped for this to work.

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#13

Re: Spline Cutting

12/18/2008 11:35 AM

Sorry I went through the site and also had a mail discussion with them. The maximum size is 1" whereas as per my first mail, the OD is 370mm (14.5")

Must try for generation on HB

Anybody tried it out on Vert lathe ? Only problem as I can see is how to maintain the axis tangential to the shaft. may have to try the item in the existing resources with some ingeneous means.

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#14
In reply to #13

Re: Spline Cutting

12/20/2008 6:38 PM

Set up horz borer as mill and cut the spline. If your load is small take time and cut it easy. Any appropriately sized index table will do for you. Follow hyperlink to example.

Maintain axis tangential to shaft use a rotary index table.

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Users who posted comments:

BlueAussieBoy (1); bwire (2); Ed Weldon (3); Keith E Bowers (1); murphyc1 (1); peter08 (3); sb (2); suresh sharma (1)

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