Your tape drive has also a capstan which went to goo over the past 30 years, so please do not just put them into the drive without fixing that first.
The following are suggestions I'm not implemented, but they seem plausible to me based on other's discussions and some related experience. Please report any results. Consider making another capstan, otherwise called a "pressure roller". In the end, it's a stiff rubber wheel on a bronze bearing with an internal diameter to fit on some roller. Examine your drive or others of same brand and model to determine dimensions. Keep in mind: it's the metal drive roller which determines tape speed, not the roller. It's possible a piece of bronze can be machined to be the correct size, then rubber molded around it, and then carefully machine the rubber to the correct diameter. There are two-part rubber compounds which when mixed and cured are quite stiff. Or, obtain another larger roller and cut it to fit. Rubber can be abraded in a lathe at low speed. Stiff rubber pieces are often sold as furniture bumpers or "corks" for pipe and "test tubes". These machining operations may require practice, and old tape drives can be found to make test rollers - as all you really need to do is drive the capstan motor and monitor tape speed for stability. Any signal on any tape can be watched on an oscilloscope and tape speed determined. A stable signal means tape speed is stable, a wriggly signal means tape speed is varying, probably at the rotation rate of the capstan pressure wheel, or rotation rate of the drive capstan, or due to other irregularities. Herb Johnson -- Herbert R. Johnson, New Jersey USA http://www.retrotechnology.com OR .net
Your tape drive has also a capstan which went to goo over the past 30 years, so please do not just put them into the drive without fixing that first.
I've had Terry's Rubber Rollers redo some pinch rollers and idler wheels for some reel-to-reel tape recorders a while back and the results were really good. It costs a few bucks, but if you want to avoid doing it yourself, or if it's a more complex part, it might be worth it: http://www.terrysrubberrollers.com David
Sorry, David, I missed this before I suggested the same thing. Thanks for sharing this. Terry gets at least 2 votes here! On Tue, Nov 17, 2015 at 10:51 AM, David Ryskalczyk via vcf-midatlantic < vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
Your tape drive has also a capstan which went to goo over the past 30 years, so please do not just put them into the drive without fixing that first.
I've had Terry's Rubber Rollers redo some pinch rollers and idler wheels for some reel-to-reel tape recorders a while back and the results were really good. It costs a few bucks, but if you want to avoid doing it yourself, or if it's a more complex part, it might be worth it: http://www.terrysrubberrollers.com
David
-- Thanks, -AJ http://MicrotechM1.blogspot.com
Hi Herb, Herb Johnson via vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
Keep in mind: it's the metal drive roller which determines tape speed, not the roller.
This is exactly why I know as well. It is just there to get the "speed on the tape" but it is not mission critical to get the dimensions 100% correct. Remember - the capstan dimensions change over time anyway because the material will be constantly removed during operating the tape. This is a normal process. IF the capstan dimensions would be vital for the correct function of the tape drive, it would have been unable to read the times not far after it was shipped - probably. So getting the capstan "as far as possible in the same size" should be enough... I had trouble opening the motor so chaning the bronze part with the capstan in a whole might be problematic - but maybe I was just lacking the right tools. It also came to my mind to look for old VCRs and see if they have fitting capstans but didn't got that far....
On 11/17/2015 12:38 PM, Oliver Lehmann via vcf-midatlantic wrote:
Keep in mind: it's the metal drive roller which determines tape speed, not the roller.
This is exactly why I know as well. It is just there to get the "speed on the tape" but it is not mission critical to get the dimensions 100% correct. Remember - the capstan dimensions change over time anyway because the material will be constantly removed during operating the tape. This is a normal process. IF the capstan dimensions would be vital for the correct function of the tape drive, it would have been unable to read the times not far after it was shipped - probably.
Actual tape speed over the head is actually not that critical for many types of tape drives. Most modulation/encoding schemes are self-clocking, either through separate clock tracks (DEC TU56) or embedded clocks that are recovered via a phase-locked loop. Getting close will do it. Speed variations, on the other hand, can be bad if a PLL is used for clock recovery. If the period of the speed variation falls outside of the clock recovery PLL's loop bandwidth, the loop could lose lock, resulting in the loss of the clock. So, keep those replacement rollers as round as possible, but don't worry so much about the exact diameter, unless you know for a fact that there is an absolute tape speed requirement, which is rare. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
On 11/17/2015 2:18 PM, Dave McGuire via vcf-midatlantic wrote:
On 11/17/2015 12:38 PM, Oliver Lehmann via vcf-midatlantic wrote:
Keep in mind: it's the metal drive roller which determines tape speed, not the roller. This is exactly why I know as well. It is just there to get the "speed on the tape" but it is not mission critical to get the dimensions 100% correct. Remember - the capstan dimensions change over time anyway because the material will be constantly removed during operating the tape. This is a normal process. IF the capstan dimensions would be vital for the correct function of the tape drive, it would have been unable to read the times not far after it was shipped - probably. Actual tape speed over the head is actually not that critical for many types of tape drives. Most modulation/encoding schemes are self-clocking, either through separate clock tracks (DEC TU56) or embedded clocks that are recovered via a phase-locked loop. Getting close will do it.
Speed variations, on the other hand, can be bad if a PLL is used for clock recovery. If the period of the speed variation falls outside of the clock recovery PLL's loop bandwidth, the loop could lose lock, resulting in the loss of the clock. So, keep those replacement rollers as round as possible, but don't worry so much about the exact diameter, unless you know for a fact that there is an absolute tape speed requirement, which is rare.
-Dave
These z8000 tapes are MFM, so they should be self-clocking, I think? -- Jonathan Gevaryahu jgevaryahu@gmail.com jgevaryahu@hotmail.com
On 11/17/2015 02:28 PM, Jonathan Gevaryahu via vcf-midatlantic wrote:
Keep in mind: it's the metal drive roller which determines tape speed, not the roller. This is exactly why I know as well. It is just there to get the "speed on the tape" but it is not mission critical to get the dimensions 100% correct. Remember - the capstan dimensions change over time anyway because the material will be constantly removed during operating the tape. This is a normal process. IF the capstan dimensions would be vital for the correct function of the tape drive, it would have been unable to read the times not far after it was shipped - probably. Actual tape speed over the head is actually not that critical for many types of tape drives. Most modulation/encoding schemes are self-clocking, either through separate clock tracks (DEC TU56) or embedded clocks that are recovered via a phase-locked loop. Getting close will do it.
Speed variations, on the other hand, can be bad if a PLL is used for clock recovery. If the period of the speed variation falls outside of the clock recovery PLL's loop bandwidth, the loop could lose lock, resulting in the loss of the clock. So, keep those replacement rollers as round as possible, but don't worry so much about the exact diameter, unless you know for a fact that there is an absolute tape speed requirement, which is rare.
These z8000 tapes are MFM, so they should be self-clocking, I think?
I think that's a reasonable assumption. MFM schemes usually use PLL-based clock recovery. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
On 11/17/2015 11:49 AM, Herb Johnson via vcf-midatlantic wrote:
Your tape drive has also a capstan which went to goo over the past 30 years, so please do not just put them into the drive without fixing that first.
The following are suggestions I'm not implemented, but they seem plausible to me based on other's discussions and some related experience. Please report any results.
Consider making another capstan, otherwise called a "pressure roller". In the end, it's a stiff rubber wheel on a bronze bearing with an internal diameter to fit on some roller. Examine your drive or others of same brand and model to determine dimensions. Keep in mind: it's the metal drive roller which determines tape speed, not the roller.
It's possible a piece of bronze can be machined to be the correct size, then rubber molded around it, and then carefully machine the rubber to the correct diameter. There are two-part rubber compounds which when mixed and cured are quite stiff.
Or, obtain another larger roller and cut it to fit. Rubber can be abraded in a lathe at low speed. Stiff rubber pieces are often sold as furniture bumpers or "corks" for pipe and "test tubes".
Most types of rubber can be machined much more easily if frozen using liquid nitrogen or dry ice. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
Not sure if I've mentioned this here before, but I've used http://TerrysRubberRollers.com quite successfully for about a dozen rollers over the past few years. He's not cheap, but he does an excellent job! All of the QIC drives I use now have rollers rebuilt by Terry. On Tue, Nov 17, 2015 at 1:13 PM, Dave McGuire via vcf-midatlantic < vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
On 11/17/2015 11:49 AM, Herb Johnson via vcf-midatlantic wrote:
Your tape drive has also a capstan which went to goo over the past 30 years, so please do not just put them into the drive without fixing that first.
The following are suggestions I'm not implemented, but they seem plausible to me based on other's discussions and some related experience. Please report any results.
Consider making another capstan, otherwise called a "pressure roller". In the end, it's a stiff rubber wheel on a bronze bearing with an internal diameter to fit on some roller. Examine your drive or others of same brand and model to determine dimensions. Keep in mind: it's the metal drive roller which determines tape speed, not the roller.
It's possible a piece of bronze can be machined to be the correct size, then rubber molded around it, and then carefully machine the rubber to the correct diameter. There are two-part rubber compounds which when mixed and cured are quite stiff.
Or, obtain another larger roller and cut it to fit. Rubber can be abraded in a lathe at low speed. Stiff rubber pieces are often sold as furniture bumpers or "corks" for pipe and "test tubes".
Most types of rubber can be machined much more easily if frozen using liquid nitrogen or dry ice.
-Dave
-- Dave McGuire, AK4HZ New Kensington, PA
-- Thanks, -AJ http://MicrotechM1.blogspot.com
participants (6)
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Dave McGuire -
David Ryskalczyk -
Herb Johnson -
Jonathan Gevaryahu -
Microtech Dart -
Oliver Lehmann