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  1. #16
    Join Date
    Apr 2012
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    Healesville
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    Quote Originally Posted by nearnexus View Post
    I don't know what you are doing wrong, but I have NEVER had chatter with any of my TPG's. TPG's after all are only kissing the work surface, so you must be really butchering/loading up the grinding medium to get chatter.
    Did you actually read what I said?

    Quote Originally Posted by shedhappens View Post
    When internal grinding depth of bore is limited to shaft and extension mandrel diameter, small dia shafts and grinding wheels chatter very easily so you can only do very short bores, when you get chatter if you are close to your target you will over shoot and throw the part over the fence.

    Rob, I will try to answer your snarky questions and accusations in a gentlemanly manner, you have to understand that not everyone in this forum just does handyman work and makes toys with cheap or donated Bangood products. Also not all members in this forum worked in IT and polished chairs for most of their career.
    I have 3 tool post grinders, 1 is home built (35 yrs ago) and rarely gets used these days, I have a cylindrical grinder so it only gets used if the job cannot be mounted between centres. The second TPG is an Italian made machine and again rarely used these days, Smaller jobs I will do in the T&CG.
    The 3rd TPG is a water cooled 2.2kw 3 ph spindle motor with an er20 chuck and VFD, this gets a fair bit of use and is used on the T&CG or one of my lathes.

    Quote Originally Posted by nearnexus View Post
    What the hell has that got to do with chatter ? Get real. You would see it in the grinding pattern first up and secondly it should NEVER happen given the very light pressures involved. LOL How much grinding have you actually done ?
    Rob. chatter is the wheel oscillating and bouncing on and of the job m8, when that happens the hole gets bigger than what you want, if you need further details.....just ask! nicely.....
    With the No 3 TPG I use a 13mm shaft for grinding deeper holes and accuracy diminishes rapidly after about 50mm in shaft length so I don't think that you would not also be getting chatter with your kmart router grinder.

    Quote Originally Posted by nearnexus View Post
    LOL How much grinding have you actually done ?
    Obviously not as much as you Rob, so do me a favor m8 put your kmart TPG on your greatest lathe in the world and see if you can finish grind a 60mm long bore .750" dia + or - .0002" in hardened 4140.
    Oh hey.....buddy....do you have something to measure it with?

  2. #17
    Join Date
    Sep 2010
    Location
    Lebrina
    Posts
    1,910

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    I may become the owner of a tool post grinder tomorrow if the person that has first dibs doesn't follow through with the purchase for whatever reason, so right about now I'm hoping that some passing alien space ship abducts them temporarily. Unfortunately, I don't have a direct line to the mother ship and I reckon I'll most likely miss out this time round.
    I am still weighing my options and I have a few ideas bouncing around my brain box. Dollar wise I reckon I can build something pretty decent for less that I can buy one - provided I don't count my time.
    I'll keep thinking and watching what comes up for sale as I don't "need" one as such and therefore I have time.
    If I did build one, I would definitely want a decent external grinding capacity, as well as the ability to grind internals such as morse tapers and such, so that puts me in the position of requiring significant speed adjustment and differing abrasive mounting options. I can easily source a .55Kw 3 phase 2 pole motor for a good price, which then leads me to power transmission options. I notice that flat belts seem to be the option that most larger TPG's use, while the smaller units seem to utilise round section polyurethane belts. Aluminium would be the best choice for pulleys I'm thinking in order to minimise imbalance issues. Timing pulleys and belts would possibly provide an off the shelf solution provided the required speed of the small arbor does not overtax them.

  3. #18
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

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    Hi Karl,

    As you probably know, I'm making a TCG and am in the throws of making a grinding spindle. It uses a 12 mm diameter shaft and is designed to spin a 100 mm abrasive wheel. The bearings that I'm using are cheap 6801ZZ ones, at less than a £1 each. I'm also going to use timing belts to drive it. Ignoring everything except materials it has cost me less than £20 (about 40 AU $) so far. I expect to spend about the same again for the pulleys, belt and sundries.

    You mention motors. Obtaining small single phase motors up to about 1Hp are no problem for me, my issue is getting one that is small and light enough to be supported on a 20 mm column. I thought I had that cracked with one that I found on Evilbay. Turned out that I misread the rating, it was only a tenth of what I thought it was.

    HTH.
    Best Regards:
    Baron J.

  4. #19
    Join Date
    Aug 2010
    Location
    Near Bendigo, Victoria, AUS
    Age
    72
    Posts
    3,102

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    Here are the first photos of the tool post and hand-held grinder I'm working on.
    As you can see, I decided not to make a motor mounting adaptor but replace one of the motor end shields with a custom made flange, so it is integrated with the handle/tool post holder.
    That handle will contain and be the heatsink for the speed controller (ESC) and the servo tester that I'm using to control the speed. More on the electrics to come.
    It was an interesting bit of milling the inside of the handle block after drilling and boring a 30mm hole to start with. The handle is around 90mm long and 45mm across each side. It will get radiuses edges so it's not too uncomfortable in the hand, but retains the flat surfaces for machine mounting.
    The whole thing feels very solid and rigid.
    I'll fit the electrics and electronics tomorrow.

    Cheers
    Joe
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

  5. #20
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    9,088

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    Be interesting to see how you get on Joe. I'd come up the same setup to add to my jig grinder, but that's a long way from happening. I do wonder how rigid it is and how the bearings will stand up. Though given how many hours a year it will be used it should likely wont have to last to long.

  6. #21
    Join Date
    Sep 2010
    Location
    Lebrina
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    I can certainly understand the challenges posed by small bores with a bit of depth to them. How do proper TPG's of quality parentage handle this issue? Let's use the example of a MT2 or MT3 internal taper as an example. If realistic, then that's the point I would like to be able to reach on the lower end. Without meaning to oversimplify the process, external grinding seems to present far fewer challenges than smallish internal bores.
    The motor I have my eye upon, should I go down the build it yourself road weights 11Kg, so I would expect the whole shooting match to come in between 20 and 25Kg (likerly closer to 20Kg), which seems reasonable on a largish lathe. As with most machine tools, weight should hopefully dampen vibration somewhat and theoretically enhance the accuracy potential, provided the weight is reasonably well balanced on the tool post mount - my theory/hope anyway. I am leaning toward ER collets for abrasive mounting at this point, but that may well be subject to the original question relating to the requirements of small internal grinding.
    Naturally, all this pondering and planning will become irrelevant should I be lucky enough to find a suitable unit to purchase.
    I wonder how popular TPG's were in the past and where they have all gone?

  7. #22
    Join Date
    Nov 2007
    Location
    melbourne australia
    Posts
    3,228

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    Quote Originally Posted by Stustoys View Post
    I do wonder how rigid it is and how the bearings will stand up.
    It looks like the motor is intended for electric buggies. I don’t know what sort of bearings they put in those.

    https://www.onestoprchobbies.com.au/...Y-MOTOR-2350KV
    Chris

  8. #23
    Join Date
    Sep 2010
    Location
    Lebrina
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    Well I've just got confirmation that the aliens didn't intervene on my behalf and I've missed out on the TPG that was for sale.
    I would really appreciate any input relating to the grinding of internal bores with a bit of depth such as internal morse tapers. Even if I hold out and purchase a TPG rather than custom building, this question is going to be relevant and steer my course somewhat.
    I have no doubt that I can construct a mount and drive system that will work for external grinding, but I am concerned about the best way to reach into small bores and avoid chatter and resultant loss of accuracy.

  9. #24
    Join Date
    Aug 2015
    Location
    Melbourne, Australia
    Posts
    843

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    Hi Karl,

    Re the internal Morse tapers. I recently set up a waldown c0 for use. One of the first projects for it is a spindle taper adapter to convert the very odd south bend spindle taper to an Mt3. The purpose being to being able to just throw in the adapter with an Mt3 dead center and do between centers turning without re cutting the center. Which is pretty tedious.

    It didn't take long to realise that a) the internal taper is deeper than the tpg spindle will go and b) the min size of wheels on the tpg internal spindle are too large to grind that internal taper.

    So, worth taking into account how one might mount normal 6mm or 1/4" grinder bits to the spindle.

    I started looking last night into er11 and/or the typical 6mm collet holders for die grinders.

  10. #25
    Join Date
    Apr 2012
    Location
    Healesville
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    Quote Originally Posted by Karl Robbers View Post
    I have no doubt that I can construct a mount and drive system that will work for external grinding, but I am concerned about the best way to reach into small bores and avoid chatter and resultant loss of accuracy.
    Karl when i have the need for a particular/important job i will make a grinding wheel extension that fits directly into the er20 collet chuck, probably hardened and then ground to reduce runout.

    For your needs you could possibly make mounted point extension shafts that screw directly onto the grinding wheel hub, make tapered one's for mt2 and mt3 or what ever dia and length that you need, within reason and a suitable material.

    Boring and reaming is usually good enough for a morse taper, sometimes I have had run out on new morse taper sleeves, I mount them on a length of stock with the required taper and gently recut the centre in the end of the sleeve as they are out of wack, then grind the outer taper using the freshly cut centre.

    I think these days if you have deep pockets you can buy carbide extension shafts and also hydraulically dampened shafts for milling and grinding.

  11. #26
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Hi Guys,

    I've rescued several MT2 and MT3 bores using a reamer, but you do have to check that they are not hardened or they will wreck the reamer in short order. Avoid 1" sleeves like the plague, the ones I have are as hard a diamond on the inside, but oddly you can turn the outside and file it.
    Best Regards:
    Baron J.

  12. #27
    Join Date
    Sep 2010
    Location
    Lebrina
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    Quote Originally Posted by shedhappens View Post
    Karl when i have the need for a particular/important job i will make a grinding wheel extension that fits directly into the er20 collet chuck, probably hardened and then ground to reduce runout.

    For your needs you could possibly make mounted point extension shafts that screw directly onto the grinding wheel hub, make tapered one's for mt2 and mt3 or what ever dia and length that you need, within reason and a suitable material.

    Boring and reaming is usually good enough for a morse taper, sometimes I have had run out on new morse taper sleeves, I mount them on a length of stock with the required taper and gently recut the centre in the end of the sleeve as they are out of wack, then grind the outer taper using the freshly cut centre.

    I think these days if you have deep pockets you can buy carbide extension shafts and also hydraulically dampened shafts for milling and grinding.
    One of the ideas that I had was along those same lines - scwewing the small arbor extensions to the main grinding shaft. I'm fairly sure that's how the TPG that I missed out on handled the task as well.
    In reality, I probably don't need that capability, however if I'm going to build one, then Ideally I want to cover as many eventualities as I can rather than wish I'd thought of it later.
    I've got a couple more avenues to chase up where I may just find a TPG, if they don't pan out then I reckon some heavy duty research and brain storming will begin and I might just build my own for the heck of it. Unfortunately, like most of us, I have several projects on the go.

  13. #28
    Join Date
    Nov 2019
    Location
    Brisbane
    Age
    69
    Posts
    452

    Default Tool post grinder

    Hello from BC.
    I just did an fleabay search for tool post grinder. Available from the USA is a new Dunmore high speed spindle with 3 flat belt pulleys. $207AUD and about $45 post. You may get cheaper delivery if you buy a USA mailbox from shipit. Mon am I will take a pic of my Cincinatti internal grinding attachment to give an idea of the proportions of shaft diameter to stick out. A big problem with internal grinding is using too large a wheel diameter. This makes the wheel try to chase the diameter and causes big chatter. When you blow up a wheel the learning curve is steep. From memory Norton abrasives specify no larger than 60% of bore size.
    regards
    BC

  14. #29
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    Sep 2010
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    Lebrina
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    If it weren't for the shipping costs getting out of hand, the USA would be able to supply us all with TPG's with some left to spare. There are quite a few suitable grinders on ebay, but the freight equals or exceeds the price for the machine even before our Government put their hand out for their 10%.
    Those spindles do provide an interesting option though.

  15. #30
    Join Date
    Nov 2019
    Location
    Brisbane
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    69
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    452

    Default USA shipping

    Quote Originally Posted by Karl Robbers View Post
    If it weren't for the shipping costs getting out of hand, the USA would be able to supply us all with TPG's with some left to spare. There are quite a few suitable grinders on ebay, but the freight equals or exceeds the price for the machine even before our Government put their hand out for their 10%.
    Those spindles do provide an interesting option though.
    Hi Karl. I was serious about shipit. $10 USD a month gets you a USA mailbox. They will hold it open for 3 months. A lot of small parcels ship in the USA for $10.00. Recently I had 3.2kg sent to me, and thru them Auspost quoted $38.00. I had to use Fedex as my daughter ordered some vitamin pills and it was declared as food. Still at $74.00 from the USA and 3 days delivery I thought it was a bargain. The limit is 22kg. When chasing bearings for my Kearns borer the local price was $1540 for 2 of them and China quality. I got new old stock from a USA surplus dealer. Made in USA many years ago but still new in packaging. $156.00 plus $40.00 to ship. You have up to $700.00 of goods before customs becomes a problem.
    Regards
    BC

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