Modeling twist drill tips

[McLeod]

[Cross-posted from the "Sharp Tool Engineering" forum]

I'm modeling a custom twist drill in Solid Edge and having trouble creating the tip features which are defined by the following standard parameters:

- lip relief angle
- chisel edge angle
- point angle

Machinery's Handbook (26th ed, p. 828) and other references define how those parameters are measured, but some of them cannot be used to create the features directly because the software uses different input parameters (e.g. pitch vs. helix angle of the flutes). I've checked some similar in-house drawings and models, but apparently I'm not the only one who's confused, because the more complex details look like they were fudged into the model, and the drawings rely heavily on note verbiage. I've also been all over the web searching for custom mfg. vendor design guides or actual models and drawings - so far I haven't found much beyond what's already available in Machinery's.

Can anyone provide some insight regarding good modeling and specification practices for this type of part? What kind of cutout features (helical, extruded, conical, etc.) best mimic the mfg. process for the geometry behind the three listed parameters?

 

[littlef8]

I'm not sure of the question you are asking? What are the dimensions or manufacuring techniques or how to model with the info you have?

It took me some time to understand the process before I was actually able to model twist drills. That's the big battle. You have to know how they are made, specifically the chisel point.

Check out this website:

http://www.mmsonline.com/articles/099805.html.

I don't have machinery handbook readily available to look at, but they were never much of a help. They give you major dimensions, but they leave out the "minor details" for manufacturing.

 

[McLeod]

littef8 -

The question is how to correctly model the tip geometry to mimic the manufacturing process.

My starting point is a plain cylindrical extrusion (flat ends, perpendicular to the axis) with two helical flute cutouts. I've tried to create the tip with extruded, conical, and helical cutouts, but none of them result in the correct geometry. In the handbook diagrams, the cutting lips of the tip are straight. However, any cutout of the fluted cylinder results in curved cutting lips as the helical surface rotates away from the leading edge.

Some of our machinists have described the process by which the cutting lips are relieved, which apparently involves a complex motion of the workpiece against the grinding tool. However, I still don't have enough information to be able to replicate the cutout in CAD.

Thanks for the article link. I've been reading through some interesting pieces in MMS Online, but had not come across that one yet.

 

[littlef8]

It's been a couple of years since I've modeled one up but you're on the right track as far as starting out with a protrusion and then applying the helical cut-outs for the two flutes. What you will want to do next is the included angle.

I need to get a hold of a handbook so I have some hard dimensions to work from to try and remember how I had tackled this. I do remember that the radial clearance wasn't too bad but it was the chisel point that I got stuck on in the beginning. I'm gonna play with this a bit and I will get back with you.

It helps if you can watch your machinist while he explains what he's doing. Sounds silly but sometimes this is what it takes to get the job done.