[AJ_Mac2001]

Well my machine has only been functional for less than a week and I'm looking at an upgrade. I used cheap all thread rod to drive my 3 axis wood router (1/2-13tpi) but want to move up to something more rigid and faster (thinking 1" ACME 5tpi rod from use-enco). Couple of questions:

1) I intend on using 4 pillow block bearings per rod (2 per end to minimize whip) and utilize double nuts on the outside of the outside bearings (does that make sense) to keep it from moving linearly.... is this legit or is there a better way with limited tools/metal working aptitude.

2) I think I'll use delrin tapped out to be the drive nut... I've heard there are cheap antibacklash nuts out there.... how much better / worse are they then periodically replacing the delrin.

3) And finally, the question I came on to ask, given that I want to tap delrin which of the following taps is more suitable.

45 USD 1"-5 R.H. USA ACME HAND TAP PLUG
Style: Finishing
Thread Size: 1-5
Rotation: Right Hand
Material: HSS
Thread Length (Inch): 2-1/2
Overall Length (Inch): 5-1/8
Number of Flutes: 4




110USD 1-5 2G 4FL R.H. USA TANDEM ACME TAP R.H.
Style: Roughing and Finishing
Thread Size: 1-5
Rotation: Right Hand
Material: HSS
Thread Length (Inch): 5-1/4
Overall Length (Inch): 10-1/8
Number of Flutes: 4


Thanks folks!
AJ

[pack rat]

Why are you going with 1"? If is TPI then you could use 1/2" ACME with multiple starts to reduce TPI. Piece of the same rod you could modify and make a tap for derlin. I would rethink the idea. To answer you question, finishing tap is used after roughing tap has gone through the hole.

[AJ_Mac2001]

My first inclination was to go with 1" because of the distance (5ft between support bearings). Woudn't 1" be stiffer and less prone to whipping/vibrating than 1/2". My max rpm would be 1000.

I terms of inertia, I've got 1100 oz/in servos so I hope the additional inertia is a non-issue.

What do you think.... am I throwing away good money?

[InventIt]

IMO, I would think 3/4" would be fine.

I remember someone posting a link to a calculator to determine shaft whip on leadscrews. That may help you decide.

I had to straighten my leadscrews. Even though they were bent only a 1/8" total, it made them whip. Now they spin really smooth.

Also, I used 2TPI on my router and can get 350IPM+. It really works great. It's not as fast as it sounds. With 1" - 5TPI your only at 200 IPM. Thats TWENTYYYYYYYYYYYYYY seconds travel time for your 5' span.

Do you need high resolution?

[pack rat]

I am having a similar dilema with leadscrews. I made one out of 3/4-10 alltread and found out that it is bent and wobbles as it turns.Unbending it I wasn't very succesful. Just recently I learned that I could use multistart ACME rod and make a tap for it using a piece of rod. So a 1/2-10 ACME with 4 starts would give me 2.5 turns per inch, therby reducing RPM of the screw and the wipping. Homemade tap have a tighter fit on derlin because they are made of same piece of rod that they are travelling on. Other people have done this. Also I have not seen any 1" ACME being used on DIY systems. In addition the 1" rod will provide greater stiffness and act as an additional axis if it is straight and aligned parallel if not than it would be a liability that will transform itself into vibration. IMO I would buy 1/2 2 or 4 start ACME screw and make my own nuts using homemade tap. Take a look at Invenit tread for his machine.

[pack rat]

He sneaked in while I was typing and he is the person that I was refering to. Cool

[fyffe555]

AJ

I made a tap from 1/2-10 acme and it worked ok on Delrin, Found it best to make it slightly tight and the screw and nut bed in and loosens up once you run it a bit. Came across a tap at a surplus store like your second example, rough then finish cut. That works much better but the first roughing cut isn't necessary in 1 1/2"delrin I think and the final finish cut was looser than i would have liked on the screw. I think option 2 would be an expensive choice. I haven't tried a commercial finish tap.

I was running my screws at >900rpm. Whip was a problem until I went to 1/2-10. Found that over 3 1/2 feet, two bearings spaced 4" at either end stiffens it nicely. I also use a thrust bearing either end for axial load.

I found that at higher speeds there was still some vibration from whip that the delrin nut alone was dealing with and this produced wear and allowed some movement. I added a bearing to either side of the Delrin nut on the carrage. This almost entirely removed the wear and vibration from whip that the delrin nut had to deal with alone. This made the biggest improvement and in test I could run that axis over 1000rpm before any whip vibration appeared. Of course I found a whole bunch of 1/2" radial and thrust bearings cheap so eight bearings to a screw wasn't an issue.

[AJ_Mac2001]

As always, thanks folks for all the insight.

Well tomorrow I'm going to play and as I watch my router go round in circles deliberate on what to do. Its a toss up between use-ecno and mcmaster carr.... just want to make sure I spend once on this upgrade and perhaps that's reason enough to go with mcmaster and spend a couple extra $.

Thanks again

AJ

[ger21]

You might want to look here:

http://www.mscdirect.com/PDF.process...=451&Keyword=Y

3/4-5 is only $26.67 for 6ft. I bought the 2 start 1/2-8 and it's nice stuff.

Gerry

[AJ_Mac2001]

Hey nice find Gerry!!

Being stuck next to the north pole was going to cost me 100 plus bucks in shiping alone from McMaster or Enco... but as luck would have it I'm into Atlanta next week for work and MSC has a store and DC there.... somebody's smiling down on me for this one!

1/2" - 8/2starts sounds like a great bet given all my bearings and such are already 1/2". Is the 1/2" a real 0.50" in terms of its fit into off the shelf 1/2" bearings? What did you do to "lock" it in place linearly? I'm a hack and thought I'd go for the double nut approach on the outboard ends of the bearings.


Did you tap your own drive nut... or buy an antibacklash one? If you tapped, did you use a homemade tap or do you have access to the real thing?

Thanks!

[ger21]

I just went out and put a caliper on it - it's .500 exactly. I haven't installed them yet, but I plan on turning the ends and making some rigid bearing blocks. I made a tap with a piece of the rod, a dremel and some small grinding stones. Worked pretty good.

Gerry

[AJ_Mac2001]

As a test, I tried grinding my 1/2"-13 allthread rod into a tap. If it worked out alright then I'd try the same when I go to Acme.

At any rate, I put a grinder bit in my router and flew at it. The pictures below show the grinder bit and the result. (sorry pics aren't very good)

I'm not sure how well it worked. The grinder (was a cone with a sharp tip) slowly wore itself out so by the end it was basically flat and correspondingly made a flat on the thread instead of a nice v groove.

Am I using the right kind of grinder?? or should this be some sort of HSS. I'm just looking for a cheap one off bit that fits my 1/4" collet. the net result was a flat area on the thread which barely qualifies as having an edge.

I think the grinder bit is the wrong thing... but don't know what is appropriate. suggestions??

[AJ_Mac2001]

one more pic

[InventIt]

This is how I made my tap. It worked good in delrin.

First step is to grind a 3" taper on one end of the rod.
Next is to grind cuts down the lenth of the rod. Cut down into the root of the screw to make room for the chips. I chucked my tap into the drill press to hold it steady for me. (Drill press OFF of course.)

I used a lathe to do the taper but a drill press on low speed while using your grinder works too.

[InventIt]

Cutting the flutes on the tap with it chucked in the drill press.

[InventIt]

Notice the angle of the cut. The cutting edge of the tap should be on the centerline or even a little positive rake would be good.