Building KEN I Rotary broaching tool

[coopertje]

Since its too cold to finish the painting work on the Tacchella grinder I decided to make a long desire happening, drilling square or hexagonal holes! There are several treads about this subject here and I decided to make the holder based on the design of KEN I. Thank you for sharing and the support so far Ken!

I will deviate a little from Kens plans because I do not have the mentioned material size available. The diameter of my holder will be 60mm instead of the mentioned 80mm in the plans. Since I am lazy I decided mine will be round instead of the more or less oval shape and last I will use the 6201 bearing with is larger and wider then the 6101.

Had a MT3-B16 shank laying around unused, nice base to start with. Tested before turing with a file how hard the material was, I was lucky it was not hard at all.
Put the shank between the centers

And turned the end down to 14mm

Next part is the bearing housing. Chucked up a piece of 60mm steel, centered it and drilled a center hole for the tailstock center

Then turned the outside to shape, leaving the diameters about 1mm bigger then planned, they will be finished later to remove machining marks it might get during the process

Parting off with tailstock center, as you can see I parted until I had about 10mm in diameter left, un-chucked the piece and cut through with the bandsaw.

Placed the piece in the 3-jaw to machine the bearing seat for the 6201 bearing, round 32.00mm in diameter and 12mm deep. Also made the internal boring.

It was not completely successful, the diameter I got at the end was 32.02mm. To much for a press fitting of the bearing, need to use lock tide instead…..

Now the part has to be swapped to turn the bearing seat for the 51202 trust bearing. To maintain centricity I decide to make some kind of collet. First turned down one side of a piece of round 40 aluminum back to 38mm. Swapped the part in the chuck, marked jaw number 1 and drilled and tapped M6 in the center. Last operation in the lathe is to chamber the hole and turn the diameter back to 34mm. Then took it to the mill to split the front side with a slit saw. As you can see I did not care too much to have an equal spacing between the cuts….

Mounted it back in the lathe and turned the diameter to 32.00mm. Now the part will have a snug fit on the collet meaning the the part can be fixed easily with the screw in the middle. Tested the runout and it was less then 0.01mm, good enough for me!

Tomorrow I will finish the bearing holder and maybe start on other parts for the holder if time allows.

Have fun, regards Jeroen

 

[vcutajar]

I will be following you every step of the way.

Vince

 

[tel]

As will I - this could be a very handy thing to do!

 

[Don1966]

I think I will follow along also. This could be a interesting project.

Regards Don

 

[ref1ection]

I'm very interested in this as well.

Ray

 

[Mawitö]

Really nice project and thanks for sharing.

Mawito

 

[coopertje]

Thank you all for your comments and interest!

For who is interested on the background of the tool and working, here is some more info on the tool designed by KEN I (also check the links in the post, lots of info to find there as I discovered after asking Ken again…sorry…)

http://www.homemodelenginemachinist.com/index.php?topic=17289.0

Made some progress today, not too much, went to the tool store this morning (needed a 10mm machine reamer, just had the conical hand version) and just took it easy the rest of the day.

Fitted the bearing holder on the collet made yesterday and turned the seat for the 55202 trust bearing. Round 32mm, 11.5mm deep and made a relieve of round 33mm at the front end of the housing.

Swapped it again and made a relieve for the 6202 bearing, did not do that yesterday. Do not know if it is required but for sure it will not hurt.

Next was the backplate that will be mounted on the MT3 shaft. Did see it before and decided to make a very simple, though very effective tool. A piece of brass with a roller bearing. Had the blank running true in some seconds!

Faced the front and made a hole of 14mm with a boring bar to have better control over the end diameter

Could not help myself, just need to see how it will look when finished….

I decided that today it was time to make the first internal MT taper in my live. Could make an adapter to finish the other side (and OD) of the backplate, but the idea is to have the backplate fixed to the MT3 shaft, place it in the adapter and turn things true. The adapter will be useful in future projects too…. Put a previous prepared (Stuart 10H build) blank in the spindle nose and have my MT3 reamer set ready (I put them very gentle on the bed to not damage them, better to have then on a piece of wood….)

And drilled a hole of 20.5mm (my god, what a difference a good drill makes….this is a resharpened professional drill, went trough like cutting butter!)

Below my set-up to set the support to the MT3 taper. Its 0.0502mm taper per mm on diameter, so the top slide should be set half this value for radius (that is what you are measuring with this set-up). I did set the taper a fraction to sharp, the final shape will be made with the reamer.

Made the taper with a boring bar as close as possible (checked many times the outer diameter, the finished taper should have a diameter of 23.825mm) and stopped turning when I reached 23.6mm. Since I had nothing to grab the reamer with my tailstock I used the reamer like below and it went really well! 20 RPM and lots of oil.

And here the MT3 shaft steady in the lathes spindle nose

That was not so hard after all, glad I took the step to make this MT3 adapter today.

Tomorrow I will make the broach holder.

Have fun, regards Jeroen

 

[Blogwitch]

Jeroen,

You really do need to invest in a set of soft jaws, especially if you are going to do more jobs like this.

They would have saved you hours on jig making and setting up, I use mine all the time. In fact I have a 3 jaw chuck set up with soft jaws permanently.

They are about the cheapest thing you can buy to get yourself into the high precision stakes.

Things are really looking good, and should really help me when eventually I get around to making one.


John

 

[coopertje]

John,

Thanks for the tip! I have a chuck with removable jaws, nice start to make a soft jaw version. Its written down on my to do list (page 5 bottom :big.

The collet I made is really quick, did not spend more then 20 minutes in total. And it will be reused many times, now the diameter is 32mm, next time when I have something smaller I just turn down this one and I am ready to go. The best for me would be a nice collet adapter, thats also on my to do list, I believe it was page 3 in the middle...

I will go the shop to make some chips on the broaching holder.

CU later, regards Jeroen

 

[Ken I]

Nice going Jeroen and thanks for letting us "look over your shoulder".

I'm watching.

I presume you are going to grind your broaches from solid 10mm HSS stock - or tool steel and harden perhaps ?

Ken

 

[coopertje]

Hi Ken,

I plan to make the broaches from silver steel (drill rod), make them to shape oversized, try to hard them and then grind to dimension and give them the relieve angle. Lets see what will happen, I am not so good at hardening… What about the front side of the broach, does that need to attention or can it be flat? I think I red somewhere that you should drill it with a oversized drill, but I think then the cutting points will become very weak.

Made a set-up which is far from perfect but with light cuts good enough. Clocked the bearing housing to 1 degree angle and took advantage to check my digital angle meter.

And the digital device is 0.2 degrees off!

Took the sharpest mill I had and started to take cuts from 0.1 deep to not stress the set-up. As you can see it cuts nice and symmetrical meaning the set-up is ok.

Here it is deburred and finished.

And then I realized I made a big mistake! I should drill and tap M6 the 2 holes in the same set-up….

Took the part to the lathe and set my indicator on center height

And try to find the higher and lower part on the face, when found marked it with a tool.

Put it back in the mill, clocked it out again a drilled and tapped the 2 holes with M6. I made blind holes so the front of the tool will look nice and clean.

Then I made the slots in the back plate

Degreased the MT3 shaft and the backplate, took the green lock tide, and pressed the parts together using the lathes tailstock. Its machinable after about 45 minutes.

While the MT3 shaft was drying I made the broach holder. Chucked up a piece of round 40mm

And turned it to dimension. its 15mm for the trust bearing and 12mm for the 6202. At the end its 11.5mm with a 1mm groove for the clip. This is just before parting off.

I was eager to test my MT3 adapter so I let the 10mm hole in the broach holes for a later moment. Removed the chuck and mounted the adapter in the spindle nose. The fit is quite well, I am happy at least

I faced the back plate and made a chamber (3mm deep) in the middle to make space for the broach holder.

Its starting to come together!

Remount the chuck and drilled the broach holder 9,8mm 20mm deep. Then took a 10mm reamer and reamed the hole to 10mm

I know they are unsafe but I just love long pieces of swarf!

Last thing for today I drilled and tapped M6 for the set-screw to hold to broach in the holder

This is what I got up to now, tomorrow I will assemble and start on the actual broach tooling

Thanks for watching, regards Jeroen

 

[Ken I]

Jeroen, I would not reccomend drilling. I have broached hundreds of thousands of holes using that design and flat faced broaches. (VW Golf / Rabbit / Jetta front strut rods all have a 7mm AF and some Audi an 8 and even 10mm - EN30B high tensile rod.)

You can concave grind the face to give it some rake - this helps a little but to be frank is just not worth the bother.

Don't go nuts on clearance - with a "frictionless" bearing set up there is no torque applied to the tool (there's going to be some) - but as the bearing wears this torque increaces and starts to drag the broach producing a spiral broach - the more clearance, the worse this tendancy.

In production practice when the go gauge went in but wouldn't go to the bottom - it was time to change the bearings.

On my drawing the broach has a 2½° included angle which gives ¼° clearance on the 1° toolholder. Also on the drawing a R1 radius at the root - this to prevent the creation of a "stress raiser" caused by a sharp edge - again this helps to reduce breakages. If you grind it in a tool and cutter grinder just offhand dress the corner of the wheel - its not critical. If you mill it do it with the cutter radius as washout (Don't mill across leaving the sharp cutter corner in the root).

Index reccomended regreaseing the bearings every shift's full production - Nuts to that we ran it until the bearings gave out (its as much trouble to change the bearings as it is to grease it and bearings are relatively cheap).

IIRC even without relubes the bearings used to last between 20000 to 50000 parts - and that was using soluable oil as coolant - it washes out the grease and is not a great lubricant for ballbearings.

The broach face needs to be smooth, the cutting edges sharp - flank finish good but not critical.

Obviously the "concentircity" of the profile to the shank needs to be good or you are going to introduce latteral forces that will want to snap the broach.

For hobby use add a dab of HP lube (the dark smelly stuff) and you should be good to go.

Hardened drill rod works well but you must temper it back - they will work fine glass hard but tend to snap if your alignment or tool concentricity isn't spot on.

Hope this helps.

Ken

 

[Don1966]

Great job jeroen I really like all your photos and explanations. Thanks for sharing with us.

Regards Don

 

[mu38&Bg#]

Jeroen, Looks great. I might make one of these as well. What kind of mill at your working with there? Seems to be a Deckel or some clone there of?

Greg

 

[steamer]

Hey Ken,

What would you think of using this on a turret lathe?

Dave

 

[Ken I]

Dave,
It works fine on a turret lathe, mill spindle etc.

Long answer version :-

When feeding from a screw or cam or power feed - you gain a mechanical advantage (over and above any drivetrain mechanical advantage) in that the drive is non-reversable - so it cogs in during the quiescent moments - the spindle torque is then translated into thrust against the non-reversable feed system as the corners of the broach dig in - so it feels like a lot less pressure than there really is.

Consequently on a mill quill or turret lathe (when hand fed) you are actually applying the force directly so it "feels" like quite a lot more - that said the intertia of the turret and quill also help in this regard - so it will seem "easier" at higher revs.

Since there is no real cutting velocity you can go nuts on revs but it is harder on the tool's bearings. Use higher revs when hand feeding a reversable drive like a mill quill or turret than when power feeding.

1000-1500 rpm for power feed, 1500+ for hand fed - when hand feeding, just apply a pressure that you are happy with and let it sink in.

Feed rates are limited - at Tan 1° x Broach Diameter - you will be cutting on the entire face and the effect of the wobbly broach is lost and you may as well just push it in. For an 8mm Hex this would equate to 0.16mm per rev - in practice you want to be about a ¼ to ½ of that figure.

As mentioned in my prior post, errors in alignment and tool concentricity give rise to latteral forces which want to snap the broach - so using a tailstock or mill quill in the extended position makes it more forgiving.
That said, my experience on very rigid machinery was relatively trouble free.

Regards,
Ken

 

[steamer]

My expectations exactly, but I hadn't tried it. Having the ability to float the tool should help also to prevent side loading

Nice design Ken, as usual :bow:

Dave

 

[Ken I]

Thanks Dave.

Jeroen, when you reamed the 10mm bore, I see you used the 3 jaw - were you using soft jaws ? is it accurate enough ?

The proof will be the measured runout on assembly against a 10mm pin.

Ken

 

[coopertje]

Thank you Ken for your effort and time to clear my doubts and answers!
I will make a test bit just to see if the tool is working, when I have my Tacchella tool grinder finished I will make some decent broaches.

When reaming the 10mm hole I used the dial indicator to check runout before drilling. It was 0.02mm which I assumed to be good enough. I will check the total runout tonight and let you know.

With a little bit of luck I will have the first results tonight!

Thank you for your support Don and Dave, appreciate it!

Greg, the mill is a Thiel 140. Its similar to a Deckel or Maho mill. I really love this machine, its very well build and very stable. Has power feed on all axis, scraped ways, SK-40 spindle nose with a drilling pinole, hydraulic axis locking and an automatic lubrication system.

CU later, regards Jeroen

 

[Ken I]

Jeroen,
0.02 is just fine - its just I have a pathological aversion to 3 jaw chucks for accurate work and never use them for finished diameter work or second op work.

Great going so far.

My earlier comments on reversable vs non-reversable applies where the drive efficiency is less than 50% then the drive is non-reversible - ie a screw driven tailstock quill - it doesn't matter how hard the work pushes back, the handwheel will not rotate backwards whereas a rack and pinnion drive can be pushed backwards with sufficient force.

That's probably cleared the murkiness to the consistency of mud ???


Ken