Cutting square shaped spiral

[FTlatheworks]

you can get live spindles for making a diy grinding fixture but it wouldn't be impossible to make a bearing block and a shaft with a reamed hole for an end mill(grub screw for the end mills with a flat) , maybe driven with a hand drill or similar small motor.

Stu

yes, but I’m looking for the easiest while still maintaining standard drill runout. I could just make a straight bar with r8 bearings and thrust washers, or I can make one that goes inside the boring bar sleeve that can be locked in with the socket head cap screws in the holder. I’m not sure what the easiest way to do it is. One guy spoke of using a mt2 to jm33 hand tightening chuck. I like that idea, but unsure of finishes and best methods to make that work. I don’t even know what jm33 is? My lathe is Morse taper 2, so I know what that is.

What are the names of these live spindles and who makes them?

 

[stupoty]

yes, but I’m looking for the easiest while still maintaining standard drill runout. I could just make a straight bar with r8 bearings and thrust washers, or I can make one that goes inside the boring bar sleeve that can be locked in with the socket head cap screws in the holder. I’m not sure what the easiest way to do it is. One guy spoke of using a mt2 to jm33 hand tightening chuck. I like that idea, but unsure of finishes and best methods to make that work. I don’t even know what jm33 is? My lathe is Morse taper 2, so I know what that is.

What are the names of these live spindles and who makes them?

This sort of thing , not necessarily that one , just an example.

I have seen some that are aimed more as tool post grinding attachments , probably a range of end fittings available.

Or you can get(or make) bearing blocks quite cheep and make a shaft for the cutter.

Stu





https://uk.banggood.com/No-Power-Sp...et-p-1980196.html?cur_warehouse=CN&ID=6301695

 

[FTlatheworks]

This sort of thing , not necessarily that one , just an example.

I have seen some that are aimed more as tool post grinding attachments , probably a range of end fittings available.

Or you can get(or make) bearing blocks quite cheep and make a shaft for the cutter.

Stu

View attachment 475657



https://uk.banggood.com/No-Power-Sp...et-p-1980196.html?cur_warehouse=CN&ID=6301695

I wonder if it would be better to buy that and attach it to qctp bxa cutter mount. Somehow attach it to a block that is milled down to 5/8x5/8. What would you do with it? My thought was to just turn a part that had a bearing and get a straight shank drill chuck and put the part through my boring bar holder, but I kinda like the idea of having a completely separate tool post mount for just a cross drilling fixture.

 

[jwmay]

You need to get a copy of this issue, and the next one. The parallel linked adjustable sine bar attachment will do what you want.

 

[FTlatheworks]

You need to get a copy of this issue, and the next one. The parallel linked adjustable sine bar attachment will do what you want.

Where can I get copies of those two issues? I have seen this old Tony’s sine bar video, but I don’t remember much except what I know from calculus and that sine bars will help you find angles and locate work. What’s it do?

 

[jwmay]

It cuts any thread pitch. What you want to do is cut a very odd thread pitch. The examples given were rifling gun barrels or cutting standard threads in metric machines. An Internet example of barrel rifling was given as 1 twist per ten inches. If it can do that, it can do what you’re wanting.

Back Issues « The Home Shop Machinist « Metalworking « Storefront « Village Press

secure.villagepress.com

Full disclosure: This project was built with a fully equipped shop. But it may offer insight into how to do what you’re wanting.

 

[stupoty]

I wonder if it would be better to buy that and attach it to qctp bxa cutter mount. Somehow attach it to a block that is milled down to 5/8x5/8. What would you do with it? My thought was to just turn a part that had a bearing and get a straight shank drill chuck and put the part through my boring bar holder, but I kinda like the idea of having a completely separate tool post mount for just a cross drilling fixture.

Drill chucks aren't recommended for holding milling cutters as they can slip out due do the cutting forces being in multiple directions. Also the JT taper holding the chuck has a good chance of coming lose during milling.

Would be fine for drilling though.

I would personally make something like that from scratch and hold the end mill with a reamed to size hole and a grub screw(purely for the total simplicity of making it) A lot of the smaller end mills have enlarged shanks so you would be able to use a few different sizes with one shank hole size.

How big of a helical square slot are you wishing to make?

Is it purely aesthetic or are you going to have a follower running in it ?

Stu

 

[evan-e-cent]

You can use an online computer program called RideTheGearTrain which you can find by entering it into a browser. This allows you to enter all the gears you own and tells you which gears to use to produce a particular pitch (or TPI). If your lathe has a gearbox you can ask the author of the program to add your gearbox to the list that is already provided. This does not cost you anything. The program actually displays a box with the maximum pitch that you can achieve.

I imagine you would choose the maximum possible pitch, and then turn a multi-start thread. That is several thread grooves (spirals) starting at different angles. e.g. for 4 spirals they would start at 0, 90,180,270 degrees apart.

The helix angle of the thread can be calculated from the pitch and the circumference of the groove. The spiral is like a triangular piece of paper wrapped around a bar. The angle of the slope on the triangle is the helix angle. I think the clearance angle on your cutting tool should be equal to or slightly greater than the helix angle.

The long side of the right triangle is equal to the circumference (Pi * D). The short side of the triangle is the pitch of the thread or spiral. The helix angle (H) is the smaller of the two angles. (the third angle is 90 degrees). Tan function is opposite over adjacent. So tan(H)=pitch / circumference.
You can use a calculator or smart phone to get the inverse tan function (sometimes written tan -1 or arcTan).
H = arcTan( pitch / circumference).

You shouldn't have much trouble grinding your own high speed steel cutting tool. It is easier than it looks, but may take a bit of trial and error. Intermittent cutting tends to break tooks, especially if you use carbide instead of high speed steel HSS, so gentle shallow cuts will be required. A motorized milling tool mounted on the tool post might be an idea alternative. See my YouTube video channel on how to make a milling grinding attachment.

I hope this is of some help! Evan.

 

[evan-e-cent]

PS:
It appears that the bar stock you are intending to cut is round, not square as others have assumed. In that case it would not require intermittent cutting and excessive forces should not be a great concern. The will be increased forces on the gear train when gearing up with a high ratio, but metal gears should be able to handle it. You could keep cuts light to be on the safe side, especially if using plastic gears. If you mounted a motorized milling tool, I don't think you have to bother with the helix angle (because the cutting tool is round, not square. The tip of the end mill can be flat to produce a groove with a square profile.)

In my YouTube video I mounted a treadmill DC motor on the cross-slide, and made an ER32 collet holder directly on the motor shaft. I have used it to cut a bronze hexagon with a cheap end mill mounted in the collet chuck. It spins up to 8,400 RPM with direct drive. Small grinders usually run faster than that, and making a shaft driven by a pulley system is probably better, but more complicated.

I use a DC motor speed controller which is described in some of my other YouTube videos.

Actually, I have been considering a similar project to make one of those threads that can handle a left hand threaded nut or right hand threaded nut, just for fun!

The ER32 collet holder may have the same tendency for the parallel shaft to slip in the collet, causing the depth of cut to change. In that case it would be possible to make a stop in the back of the collet to prevent it from slipping inwards during heavy loads.

 

[FTlatheworks]

Drill chucks aren't recommended for holding milling cutters as they can slip out due do the cutting forces being in multiple directions. Also the JT taper holding the chuck has a good chance of coming lose during milling.

Would be fine for drilling though.

I would personally make something like that from scratch and hold the end mill with a reamed to size hole and a grub screw(purely for the total simplicity of making it) A lot of the smaller end mills have enlarged shanks so you would be able to use a few different sizes with one shank hole size.

How big of a helical square slot are you wishing to make?

Is it purely aesthetic or are you going to have a follower running in it ?

Stu

I’m not milling like that. This is a cross drilling jig only and completely separate from the spriral groove cutting project. It’s another option for drilling out knobs, or cross drilling in a spiral pattern kind of like a slotted rotor, but the holes will be drilled in the side of the stock.

Idk though, now you have me thinking should I do it the way you said with a grub screw and end mill? I have seen people do routers and milling type attachments to cross slide, but I never paid them any mind because I figured the quality and rigidity would be extremely low.