Author Topic: A thing..... (Read 43400 times)

bogstandard · « **Reply #25 on:** March 24, 2009, 02:11:55 AM »

Darren,

We all have our own little ideas of getting things done in the shop, so you do it how you want to.
There are no hard and fast rules, so if it suits you, DO IT.

It is always a good idea to have interchangeability, I have done it between my lathe and RT on the mill. It works for me.

John

Stilldrillin · « **Reply #26 on:** March 24, 2009, 03:22:46 AM »

Good thinking, and blummin well done Darren!

raynerd · « **Reply #27 on:** September 06, 2009, 08:23:48 PM »

Hey Darren, I`ve viewed this topic many times over the last few weeks as I have been concentrating on my workshop and machines and getting everything running as I want it before I go any further with engine builds etc. I have decided to make a QCTP like this and just have a couple of questions. I`m going to be using a round bar of steel rather than a block like you did, only because that is the scrap I found and was given free from the scrap heap!
1. Can I ask about your off centre bore in the main body of the tool post, was this simply to give more clearence when the two sides where taken down to size? I guess if it had been central, once the centre spigot and cam were fitted it would have got near to the edge of the dovetails/sides right?

2. Also, most QCTP have two sides each dovetailed to accept a holder when needed for turning or facing, so a side on the left and a side on the front. I noticed that you have cut flats on two sides but only dovetailed one. Is there any reason you didn`t put a dovetail on the second side so as to gain to working faces?

3. The dovetails themselfs are 60deg or did you use 55deg because of your cutting tool - either way, I mentioned a 60deg dovetail in my latest thread here: http://madmodder.net/index.php?topic=1731.msg17115#new and Jonny gave a reason why it may be more suitable to use 45deg dovetails. I`ll be honest that I`m still not 100% sure why I would have to be more accurate cutting 60deg dovetails than 45deg dovetails but if this is the case, do you think the 45deg would be more suitable?

Anyway, hope you can help. I wasn`t a member on here when you posted this thread so just wanted to say nice job and hope mine turns out as well. I`d be chuffed if it did!

Darren · « **Reply #28 on:** September 07, 2009, 04:54:13 AM »

Quote from: craynerd on September 06, 2009, 08:23:48 PM

Hey Darren, I`ve viewed this topic many times over the last few weeks

Really....., well you don't seem to have understood it very well cos most of what you wrote is wrong.........

Most of the answers to your q's are in the posts, have another read, slowly this time, and come back with anything you are still unsure of and I'll only be too happy to help..

NickG · « **Reply #29 on:** September 07, 2009, 05:35:26 AM »

Chris,

I think the following is right but somebody please correct me if I'm wrong!

On the accuracy thing, I think Jonny is right in that you would need to be more accurate machining the 60 deg dovetails. Pythag tells you that with a 60 deg dovetail, say if you make the dovetail 1mm too wide (exaggerated for purposes of explaination) that will allow the holder to move 1 x tan60 outwards, i.e. 1.73mm. With a 45 deg dovetail, 1mm deviation would allow the thing to move out 1mm, since tan45 = 1.

Also, Jonny mentioned repeatability. When you clamp the holder up with the 60 deg dovetail the variation on how far it pushes outwards is likely to be greater as a smaller component of the force is acting directly inwards. As he said, difficult to explain, will try to knock up a CAD sketch for you tonight if you are still struggling.

Although it never occurred to me before, 45 deg would be better.

Nick

raynerd · « **Reply #30 on:** September 07, 2009, 08:05:59 AM »

Quote

well you don't seem to have understood it very well cos most of what you wrote is wrong

Correct Darren, I must not have understood because I can`t find anything that explains why you bored in the main shaft off centre and anything stating why you have no dovetails on the front face in addition to the side. You do mention something about your compound slide being high but I don`t see how this effects having a front face for tool holding as well as the side. You do discuss in a little detail the issue of the dovetail angle but not that I understand it. However that said, I think with NickG explanation I understand a little more why 45deg dovetails would allow more error.

So, sorry, I have read and even printed this thread out and I can see you are unwilling as most would be to retype info already printed, but I just can`t find it and would really like to know! No doubt you will be able to embarrass me and quote your posts where the info I require is printed but if it is there, I obviously don`t understand.

Sorry, Chris

Cheers NickG - if you have time for something on CAD it would be useful!

Darren · « **Reply #31 on:** September 07, 2009, 08:23:35 AM »

Chris I am not unwilling at all, it's just that it seems you have not read the thread and it could answer most of your questions?

Here goes then...

Quote from: craynerd on September 06, 2009, 08:23:48 PM

Hey Darren, I`ve viewed this topic many times over the last few weeks as I have been concentrating on my workshop and machines and getting everything running as I want it before I go any further with engine builds etc. I have decided to make a QCTP like this and just have a couple of questions. I`m going to be using a round bar of steel rather than a block like you did, only because that is the scrap I found and was given free from the scrap heap!

I didn't use a block, I cut a section from a round pin

Quote from: craynerd on September 06, 2009, 08:23:48 PM

1. Can I ask about your off centre bore in the main body of the tool post, was this simply to give more clearence when the two sides where taken down to size? I guess if it had been central, once the centre spigot and cam were fitted it would have got near to the edge of the dovetails/sides right?

My round bar was not big enough for two dovetails (you don't need two anyway) and I gained more clearance for machining by offsetting the mounting hole

Quote from: craynerd on September 06, 2009, 08:23:48 PM

2. Also, most QCTP have two sides each dovetailed to accept a holder when needed for turning or facing, so a side on the left and a side on the front. I noticed that you have cut flats on two sides but only dovetailed one. Is there any reason you didn`t put a dovetail on the second side so as to gain to working faces?

Explained above

Quote from: craynerd on September 06, 2009, 08:23:48 PM

3. The dovetails themselfs are 60deg or did you use 55deg because of your cutting tool - either way, I mentioned a 60deg dovetail in my latest thread here: http://madmodder.net/index.php?topic=1731.msg17115#new and Jonny gave a reason why it may be more suitable to use 45deg dovetails. I`ll be honest that I`m still not 100% sure why I would have to be more accurate cutting 60deg dovetails than 45deg dovetails but if this is the case, do you think the 45deg would be more suitable?

I didn't use 55deg dovetails, I made 60deg ones....it's in the text.

Quote from: craynerd on September 06, 2009, 08:23:48 PM

Anyway, hope you can help. I wasn`t a member on here when you posted this thread so just wanted to say nice job and hope mine turns out as well. I`d be chuffed if it did!

Hope that help Chris....

NickG · « **Reply #32 on:** September 07, 2009, 10:27:58 AM »

Chris,

I can't see the advantage of having 2 dovetails either, you can just swing it around the other way if you really need to and turn the tool round in its holder.

Nick

raynerd · « **Reply #33 on:** September 07, 2009, 02:27:48 PM »

Cheers Darren, I know I`m a pain in the ars3 but you`ve helped a lot. I think the biggest reason I looked a t1t is because I said, "I`m going to be using a round bar of steel rather than a block like you did,...! " I said it the wrong way around, I have a block and I know you used round - sorry, that probably did look daft!

I know that you don`t need both front and side faces machined to accept a tool holder but it is a little more convienient. I guess I need to plan out and see what layout is best. I`m still not totally clear about the 45deg V 60deg dovetails but I guess it seems that 45deg would be better/easier. I was actually looking at the QRTP sold by RDG and the clamping mechanism is quite strange - it isn`t just a straight dovetail.

Anyhow, perhaps it is time to get this talking into swarf! Arc Euro actually has some dimension shown for their QCTP so I may use those.

Thanks again, and sorry for being a pain.

Chris

NickG · « **Reply #34 on:** September 07, 2009, 06:00:46 PM »

Chris, haven't had a chance to do the CAD sketch to explain yet but I will. A picture is worth 1000 words in this case.

I still don't see how it's any better with 2 on really, you wouldn't leave 2 tools on as they'd prob get in the way.

The RDG ones are dickinson style posts, it's not really a dove tail, bit more like a T slot and the cam pulls a T back towards the main block pulling the T slotted holder with it and clamping against the block.

Not sure if these are better or piston type? 6 & 2 3's ?

Nick

jgroom · « **Reply #35 on:** September 08, 2009, 12:28:43 PM »

Hi all. IIRC 60deg dovetails are preferred for mill tables and such because they have a larger bearing surface than 45deg, larger oil film, better wear, etc. That being said I don't see why a 45deg wouldn't work fine in a toolholder. I had a (homemade) 2 dovetail holder on my 9" SB and it was handy, but it was also bulky and a real PITA when working close to the chuck. It has since been replaced with a single dovetail unit which works much better (and needs painted

)

Thanks
Jeff

Darren · « **Reply #36 on:** September 08, 2009, 12:39:01 PM »

Quote from: jgroom on September 08, 2009, 12:28:43 PM

I had a (homemade) 2 dovetail holder on my 9" SB and it was handy, but it was also bulky and a real PITA when working close to the chuck. It has since been replaced with a single dovetail unit which works much better (and needs painted )

Thanks
Jeff

That's a very good point there Jeff, you sure can get close and keep overhangs a little shorter without the second dovetail getting in the way.....

raynerd · « **Reply #37 on:** September 08, 2009, 04:22:35 PM »

Thanks for that Jeff - very good point and thanks for the pictures.

I`ve just made a start, had an hour cleaning up the scrap steel I just got tonight. I actually was going to use a block but I found a round bar yesterday at the srappy so will use that. It is my first time working with steel and as expected it was much different than working with brass or ally that I have been working with. The top layer was pretty hard but once I`d broke into that it started maching quite easily. Well we`ll see how it goes.... After your thoughts and experiences with a two dovetail holder, I think I`ll actually change my mind at stick to one. Like you said, you simply loosen and swing it around when you need to.

Chris

NickG · « **Reply #38 on:** September 08, 2009, 05:55:03 PM »

Nice 1 Chris! Be sure to write it up in another thread!

Darren · « **Reply #39 on:** September 08, 2009, 06:54:29 PM »

Or just write it up here you like, makes it easier for peeps to find all the different ways of tackling the same subject in one place...

Just a thought, your call of course

bogstandard · « **Reply #40 on:** September 08, 2009, 07:11:05 PM »

I think you will find that there is a reason for having two lock on faces for a modern toolpost.

As previously mentioned, the dovetails are usually 60 degree, that is to give more surface area for clamping and so aid rigidity.

Now to the two sides.

Having a single sided holder and swinging it about is harking back to the days of lantern toolposts and HSS or carbon ground up tooling. This is where the tool tip is swung about until the angles and height look correct and the tool is used like that.

The modern way of tooling use is the tipped variety, and they really do rely on being set at the correct angle to the job for them to cut efficiently. Thousands of design hours have gone into doing just that. So the toolpost is set to 90 degs for one face and parallel to the workpiece on the other, then locked up solid. I find that using this criteria for ground tooling works just as well, and only requires the toolpost moving on very rare occasions, just to give me a bit of deep cutting clearance.

Look at almost any good tipped tooling set, and you will see they have shaped holders. When those are mounted into a squared toolpost, the tips of the tool are at the correct cutting angles to the job, and should be left that way.

Bogs

NickG · « **Reply #41 on:** September 09, 2009, 04:57:47 AM »

Good point John, I always use HSS and am always swinging the tool post about. Even a 4 way post is far better than the single one I have - it's awful!

raynerd · « **Reply #42 on:** September 09, 2009, 01:39:50 PM »

Hi John, that is interesting and makes sense to me. I`m forever swinging the tool post around to gain a better cutting angle for my HSS tools. I think perhaps much of it is lack of experience but I can certainly see when I have it set at a better angle, just trial and error and I see it cuts better. I`ve not got any indexable or "expensive" tooling but can see how these are set to the correct angle to be mounted in one of the faces of a two face QCTP with the post set square to the work.

I guess after reading that, for now I`m going to have to continue to swing the tooling around as I don`t know how to mount or grind my tooling correctly so as to set it up in a modern two face QCTP. I suppose there will be little benefit of having two faces as I have already admitted that I will probably have to continue to swing it occasionally anyway, so I guess swinging it horizontal to the work is little extra effort. That being said a single faced QCTP will still be much quicker and more effecient so this project is still all go....

Darren - if you don`t mind me posting here then I will do! I`ll get some picks up tonight -

Chris

Brass_Machine · « **Reply #43 on:** September 09, 2009, 02:16:22 PM »

Don't know how I missed this. Looks good Darren. You did a fantastic job!

Eric

Darren · « **Reply #44 on:** September 09, 2009, 06:15:33 PM »

Wow Eric, where you been

Thanks for the comments, the fact that I'm still using it and it's the only tool post used on my main lathe must mean it worked

In fact I was lathing something up earlier this evening....

John Hill · « **Reply #45 on:** September 09, 2009, 06:47:33 PM »

Hom hum, I guess I am on the outer again!

I use the original four-way thing the lathe came with and I use a collection of different sized tools that have came my way through various routes which I fear may not fit well into a QCTP?

Of course changing tools can be a pain as almost all of them need packing in one way or another but I have almost learned which packers are used with each tool.

Darren · « **Reply #46 on:** September 09, 2009, 09:06:16 PM »

It no bad thing John, I still feel the standard four way post gives a more solid hold on tooling than either of my two QCTP's.

NickG · « **Reply #47 on:** September 10, 2009, 03:21:53 AM »

The problem for me with the HSS is, it's ok finding packing but depending on where you put it, and how much you tighten the screws up varies the height. Also, when regrinding the tools it changes the height. A QCTP would make things so much quicker for me.

For the home workshop I still need the versatility of being able to swing the toolpost around. Maybe for CNC's and things they can be set rigidly parallel and normal to the spindle axis and let the tipped / indexible tooling holders deal with the angles.

Nick

bogstandard · « **Reply #48 on:** September 10, 2009, 03:42:20 AM »

Nick,

If you are going to be predominantly using HSS, you should really be looking at a lantern type toolholder.

http://cgi.ebay.com/ATLAS-CRAFTSMAN-10-12-LATHE-LANTERN-TOOL-POST-&-WRENCH_W0QQitemZ280394302671QQcmdZViewItemQQimsxZ20090907?IMSfp=TL090907187002r5035

They are very old technology, but just by loosening one top screw, the tip of the tool can be swung into almost any position within seconds.

Not as rigid as a normal toolpost, but very fast to use.

Bogs

NickG · « **Reply #49 on:** September 10, 2009, 03:49:27 AM »

Bogs, I did consider those but to get the centre height you're changing the rake angle. Suppose you just grind the tools to account for that though?

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Author Topic: A thing..... (Read 43400 times)

bogstandard

bogstandard

bogstandard