Valve seat cutter sharping jig

[Randall Va]

Goodsons has discontinued a jig used to lap seat cutters on a diamond lap thats on a kwik way boring bar,a buddy let me borrow his and I am going to make one,it not a hard project,however it needs to be precision,I need to bore a .500 hole straight with a 3 degree angle,can I use the degree scale on my mill or is there a better way to set the degree,Thanks

[John Evans]

Sine bar,gauge blocks and a DTI on the spindle . I think you will find the degree markings on the mill head are not that accurate. A 3* angle block and a DTI will also work.

[pete]

Plus one on what John said. Those degree scales are only for getting somewhat close. They aren't meant to be used when any reall accuracy is needed. There might be other ways I don't know of, but I'm quite sure if there are, they'd be quite expensive. But I don't know of a more accurate method than a good sine bar and gage blocks.

Pete

[Randall Va]

Thanks ,have never used a sine,how would I make the set up?

[Randall Va]

Looked on e bay,sine bar anywhere from 15.00 dollars on up,what would be good for this project?again thanks!

[pete]

Randall,
Exactly how accurate do you need to be with that 3 degree setting? My Machinery's Handbook lists a block height for a 5" sine bar of .26168" to give you that 3 degrees. So depending on your actual requirements and just how close you need to be to that perfect 3 degrees, you could use everything from a shop built sine bar and just a milled and closely measured block of around .261" in height, to more than a few hundred for something like a Suburban built sine bar and another couple of thousand for a good set of gage blocks.

There's a couple of ways to do the setup depending on your part size. Can you set your part to the 3 degrees in the mills vise? Or do you have to rotate the mills head over? I've never used or even seen the tooling your wanting to build, so I can't visulise it.

It would be better to Google it, but in a nutshell. A sine bar works on pure math to give you a very fast and more than clever method to obtain very accurate angles. Whoever first thought of it was a hell of a lot smarter than I am. Most of the sine tables I've ever seen are for the 5" bars although there's other sizes built such as 10" and 20" bars. So how it works. They use hardened and ground rolls that are very closely measured so each roll is the exact same diameter, or as close as they can get. The bar is notched very accurately on the expensive sine bars so that the C/L of each of those rolls is as close to 5" apart as they can get. The rolls are then screwed down into the bar to hold them in place. So with that bar resting flat on each roll you should have a line contact exactly 5" apart under the rolls. To get your 3 degree angle on the bar, you place a combination of gage blocks that will give you the .26168" stack height under one of the sine bars rolls. An instant 3 degrees set on the sine bar. Or as close to exactly 3 degrees as all the little inaccuracy's in the bar and stack height will allow. But with even a well built shop made bar and milled block, your going to be very very close to that 3 degrees.

So if your part has a flat bottom for a referance surface and it's small enough to fit in the mills vice, you'd set the preset sine bar in the mill vise, set your part on top of the bar and then clamp it at that angle in the vise. If you've got to rotate the mills head over you'd need to set the block up so it's square to one of the tables travels, (usually the X axis) and then use either a dial indicator or 10ths reading test indicator in the mills spindle to sweep across both ends of the sine bar. Once the indicator reads zero at each end of the block your head is set to the 3 degrees. It all sounds quite complicated, but once you've used this method there's no other faster or better way of obtaing very accurate angles that I know of unless your using very good and very expensive angle blocks that will give you the exact angle you need.

But I'm starting to think you have a little bit of room to fudge that 3 degrees a bit. Maybe just a cheap set of offshore angle blocks would be good enough for what your doing?

Pete

[Randall Va]

Thanks,a buddy let me borrow his sine and gage blocks and I understand now how the setup works!,he also let me use his Starrett tram gauges to tram in mill and a 6" flat ground surface plate to put in my vise to tram off of however my vise only opens to 5" what would be the best way to tram this setup? Sine bar is 15/16th and I have a 10th dti with the sine only 15/16 will that be wide enough to tram the y axis?

[GlennW]

Easiest way may be to tram the head square to the table, then indicate the fixed vise jaw parallel to the X axis, then hold the part in the vise and tilt the part three degrees using the sine bar as a reference and sweeping it with a DTI in the spindle.

Perhaps your friend has a Sine Vise...that would be even easier.

Without seeing the part, it's only a guess.

[Randall Va]

Finished my project today!!Learned how to do a angle using sine bar and gage,Thanks for the help!!Randall

[pete]

Glad we could all help, a pretty clever and well thought out system ehh?

Pete

[Randall Va]

Glad we could all help, a pretty clever and well thought out system ehh?

Pete

you said that right!!

[pete]

Well just an addition to how you and I do would do things. It's my understanding that a large commercial shop would never subject there high quality gauge blocks to the wear and tear while setting up and doing jobs exactly like yours. I guess they either use a cheaper set of shop blocks, preset the part in a vice on the surface plate, then transfer it back to the mill, or build fixtures when it's worth it for multiple part production. For us and since we don't do it very much, and were probably much more careful since were usually paying for the equipment. Then we can get away with it. But AFAIK it's not the best or even recommended practice to do it this way.

Pete